Atmel AT91SAM9G20 Embedded Processor featuring an ARM926EJ-S™ ARM® Thumb® Core

Some of the various functions are realized by multiplexing connector pins; therefore not all functions may be used at the same time (see Appendix D, Stamp9G20 Pin Assignment)).

The Stamp9G20 was designed as a flexible CPU-Module, which can be connected to base boards via 2x 100-pin fine pitch low profile Hirose® FX8 connectors

The size of the Stamp9G20's PCB is only 53x38x6.1 mm fitting it in even the smallest design. While having implemented the sensible CPU, SDRAM and Flash design it still exports almost all possible CPU-Pins on it's connectors to allow a flexible design on base boards

The Stamp9G20 has a on-board Micro SD-Card slot, thus supporting even large memories needs in its compact design

The AT91SAM9G20 runs at 396 MHz with a memory bus frequency of 132 MHz.

Here are some of the most important features of the SAM9G20 ARM926EJ-S core:

Some of these features - like Jazelle - are currently not supported by the operating system of the product.

The Stamp9G20 is equipped with 32-Bit CPU-bus. Only a 16-Bit bus is exported on the interface connectors of the Stamp9G20. The memory bus voltage is 1.8 V and runs at 132 MHz. The memory bus voltage is different from normal operating voltage, which is 3.3 V. This has to be considered, when designing additional peripherals connected to the memory bus. Eventually buffer chips are necessary.

The bus matrix of AT91SAM-controllers allows many master and slave devices to be connected independently of each other. Each master has a decoder and can be defined specially for each master. This allows concurrent access of masters to their slaves (provided the slave is available).

The bus matrix is thus the bridge between external devices connected to the EBI, the microcontroller's embedded peripherals and the CPU core.

The core features of the Advanced Interrupt Controller are:

Moreover, all PIO lines can be used to generate a PIO interrupt. However, the PIO lines can only generate level change interrupts, that is, positive as well as negative edges will generate an interrupt. The PIO interrupt itself (PIO to AIC line) is usually programmed to be level-sensitive. Otherwise interrupts will be lost if multiple PIO lines source an interrupt simultaneously.

On the Stamp9G20 IRQ0, IRQ2 and the FIQ are available. The list of peripheral identifiers, which are used to program the AIC can be found in Table B.1, “Peripheral Identifiers”

The following parts of the AT91SAM9G20 Processor can be backed-up by a battery:

It is recommended to always use a backup power supply (normally a battery) in order to speed up the boot-up time and to avoid reset problems.

The embedded microcontroller has an integrated Reset Controller which samples the backup and the core voltage. The presence of a backup voltage (VDDBU) when the card is powered down speeds up the boot time of the microcontroller.

Every Stamp9G20 has a unique 48-bit hardware serial number chip which can be used by application software. The chip is a Dallas® one-wire-chip. A Linux driver is provided. Additionally it functions as the 128 Byte EEPROM.

The Real-time Timer is a 32-bit counter combined with a 16-bit prescaler running at Slow Clock (SLCK = 32768 Hz). As the RTT keeps running if only the backup supply voltage is available, it is used as a Real-time clock.

The RTT can generate an interrupt every time the prescaler rolls over. Usually the RTT is configured to generate an interrupt every second, so the prescaler will be programmed with the value 7FFFh.

The RTT can also generate an alarm if a preprogrammed 32-bit value is reached by the counter.

The Stamp9G20 features two blocks of timer counters with three counters each. Due to multiplexing four timer counters may be used with external signals.

The TC consists of three independent 16-bit Timer/Counter units. They may be cascaded to form a 32-bit or 48-bit timer/counter. The timers can run on the internal clock sources MCK/2, MCK/8, MCK/32, MCK/128, SLCK or the output of another timer channel. External clocks may be used as well as the counters can generate signals on timer events. They also can be used to generate PWM signals.

The PIT consists of a 20-bit counter running on MCK / 16. This counter can be preloaded with any value between 1 and 2²⁰. The counter increments until the preloaded value is reached. At this stage it rolls over and generates an interrupt. An additional 12-bit counter counts the interrupts of the 20 bit counter.

The PIT is intended for use as the operating system’s scheduler interrupt.

The watchdog timer is a 12-bit timer running at 256 Hz (Slow Clock / 128). The maximum watchdog timeout period is therefore equal to 16 seconds. If enabled, the watchdog timer asserts a hardware reset at the end of the timeout period. The application program must always reset the watchdog timer before the timeout is reached. If an application program has crashed for some reason, the watchdog timer will reset the system, thereby reproducing a well defined state once again.

The Watchdog Mode Register can be written only once. After a processor reset, the watchdog is already activated and running with the maximum timeout period. Once the watchdog has been reconfigured or deactivated by writing to the Watchdog Mode Register, only a processor reset can change its mode once again.

The Peripheral DMA Controller (PDC) transfers data between on-chip serial peripherals and the on- and/or off-chip memories. The PDC contains unidirectional and bidirectional channels. The full-duplex peripherals feature unidirectional channels used in pairs (transmit only or receive only). The half-duplex peripherals feature one bidirectional channel. Typically full-duplex peripherals are USARTs, SPI or SSC. The MCI is a half duplex device.

The user interface of each PDC channel is integrated into the user interface of the peripheral it serves. The user interface of unidirectional channels (receive only or transmit only), contains two 32-bit memory pointers and two 16-bit counters, one set (pointer, counter) for current transfer and one set (pointer, counter) for next transfer. The bidirectional channel user interface contains four 32-bit memory pointers and four 16-bit counters. Each set (pointer, counter) is used by current transmit, next transmit, current receive and next receive.

Using the PDC removes processor overhead by reducing its intervention during the transfer. This significantly reduces the number of clock cycles required for a data transfer, which improves microcontroller performance. To launch a transfer, the peripheral triggers its associated PDC channels by using transmit and receive signals. When the programmed data is transferred, an end of transfer interrupt is generated by the peripheral itself. There are four kinds of interrupts generated by the PDC:

The "End of Receive Buffer" / "End of Transmit Buffer" interrupts signify that the DMA counter has reached zero. The DMA pointer and counter register will be reloaded from the reload registers ("DMA new pointer register" and "DMA new counter register") provided that the "DMA new counter register" has a non-zero value. Otherwise a "Receive Buffer Full" or, respectively, a "Transmit Buffer Empty" interrupt is generated, and the DMA transfer terminates. Both reload registers are set to zero automatically after having been copied to the DMA pointer and counter registers.

The Debug Unit is a simple UART which provides only RX/TX lines. It is used as a simple serial console for Firmware and Operating Systems.

The JTAG unit can be used for hardware diagnostics, hardware initialization, flash memory programming, and debug purposes. The JTAG unit supports two different modes, namely the "ICE Mode", and the "Boundary Scan" mode. It is normally jumpered for "ICE Mode".

JTAG interface devices are available for the unit. However, the use of them is not within the scope of this document.

The TWI is also known under the expression "I²C-Bus", which is a trademark of Philips and may therefore not be used by other manufacturers. However, interoperability is guaranteed. The TWI supports both master or slave mode.

The TWI uses only two lines, namely serial data (SDA) and serial clock (SCL). According to the standard, the TWI clock rate is limited to 400 kHz in fast mode and 100 kHz in normal mode, but configurable baud rate generator permits the output data rate to be adapted to a wide range of core clock frequencies.

The Stamp9G20 features a onboard Micro-SD-Card slot, which is connected to the MCI-A interface of the microcontroller. Please note that this is the same slot used on the Evaluation Board, so only one interface can be used at a time. Also operating systems like Linux do not necessarily support all features of the hardware unit.

The MultiMedia Card Interface (MCI) supports the MultiMedia Card (MMC) Specification V3.11, the SDIO Specification V1.1 and the SD Memory Card Specification V1.0.

The MCI includes a command register, response registers, data registers, timeout counters and error detection logic that automatically handle the transmission of commands and, when required, the reception of the associated responses and data with a limited processor overhead. The MCI supports stream, block and multi-block data read and write, and is compatible with the Peripheral DMA Controller (PDC) channels, minimizing processor intervention for large buffer transfers.

The MCI operates at a rate of up to Master Clock divided by 2 and supports the interfacing of 2 slot(s). Each slot may be used to interface with a MultiMediaCard bus (up to 30 Cards) or with a SD Memory Card. Only one slot can be selected at a time (slots are multiplexed). A bit field in the SD Card Register performs this selection.

The SD Memory Card communication is based on a 9-pin interface (clock, command, four data and three power lines) and the MultiMedia Card on a 7-pin interface (clock, command, one data, three power lines and one reserved for future use). The SD Memory Card interface also supports MultiMedia Card operations. The main differences between SD and MultiMedia Cards are the initialization process and the bus topology.

The Stamp9G20 integrates two USB host ports supporting speeds up to 12 MBit/s.

The USB Host Port (UHP) interfaces the USB with the host application. It handles Open HCI protocol (Open Host Controller Interface) as well as USB v2.0 Full-speed and Low-speed protocols.

The USB Host Port integrates a root hub and transceivers on downstream ports. It provides several high-speed half-duplex serial communication ports. Up to 127 USB devices (printer, camera, mouse, keyboard, disk, etc.) and an USB hub can be connected to the USB host in the USB "tiered star" topology.

The Stamp9G20 integrates one USB device port supporting speeds up to 12 MBit/s.

The USB Device Port (UDP) is compliant with the Universal Serial Bus (USB) V2.0 full-speed device specification. The USB device port enables the product to act as a device to other host controllers.

The USB device port can also be implemented to power on the board. One I/O line may be used by the application to check that VBUS is still available from the host. Self-powered devices may use this entry to be notified that the host has been powered off. In this case, the pullup on DP must be disabled in order to prevent feeding current to the host. The application should disconnect the transceiver, then remove the pullup.

The EMAC module implements a 10/100 MBit/s Ethernet MAC compatible with the IEEE 802.3 standard using an address checker, statistics and control registers, receive and transmit blocks, and a DMA interface.

The address checker recognizes four specific 48-bit addresses and contains a 64-bit hash register for matching multicast and unicast addresses. It can recognize the broadcast address of all ones, copy all frames, and act on an external address match signal.

An individual 48-bit MAC address (ETHERNET hardware address) is allocated to each product. This number is stored in flash memory. It is recommended not to change the MAC address in order to comply with IEEE Ethernet standards.

To completely implement ethernet an additional physical layer interface is needed (PHY). A sample implementation is found on the Adaptor Board.

The Stamp9G20 has up to six independent USARTs, not including the debug unit.

The Universal Synchronous Asynchronous Receiver Transceiver (USART) provides one full duplex universal synchronous asynchronous serial link. Data frame format is widely programmable (data length, parity, number of stop bits) to support a maximum of standards. The receiver implements parity error, framing error and overrun error detection. The receiver time-out enables handling variable-length frames and the transmitter timeguard facilitates communications with slow remote devices. Multidrop communications are also supported through address bit handling in reception and transmission.

The USART supports the connection to the Peripheral DMA Controller, which enables data transfers to the transmitter and from the receiver. The PDC provides chained buffer management without any intervention of the processor.

Six different modes are implemented within the USARTs:

RS485.  In RS485 operating mode the RTS pin is automatically driven high during transmit operations. If RTS is connected to the "enable" line of the RS485 driver, the driver will thus be enabled only during transmit operations.

Hardware Handshaking.  The hardware handshaking feature enables an out-of-band flow control by automatic management of the pins RTS and CTS. The receive DMA channel must be active for this mode. The RTS signal is driven high if the receiver is disabled or if the DMA indicates a buffer full condition. As the RTS signal is connected to the CTS line of the connected device, its transmitter is thus prevented from sending any more characters.

ISO7816.  The USARTs have an ISO7816-compatible mode which permits interfacing with smart cards and Security Access Modules (SAM). Both T=0 and T=1 protocols of the ISO7816 specification are supported.

IrDA.  The USART features an infrared (IrDA) mode supplying half-duplex point-to-point wireless communication. It includes the modulator and demodulator which allows a glueless connection to the infrared transceivers. The modulator and demodulator are compliant with the IrDA specification version 1.1 and support data transfer speeds ranging from 2.4 kb/s to 115.2 kb/s.

Signals of the Serial Interfaces.  All UARTs/USARTs have one receiver and one transmitter data line (full duplex). Not all USARTs are implemented with full modem control lines. Furthermore the available lines depend largely on the used multiplexing. Most modem control lines can be implemented with standard digital ports.

Hardware Interrupts.  There are several interrupt sources for each USART:

Please refer to the chapter about the DMA unit (PDC) for a description of the "Buffer Full" and "End of Receive / Transmit Buffer" events.

The Stamp9G20 features two SPI ports, each of them with three chip selects.

The Serial Peripheral Interface (SPI) circuit is a synchronous serial data link that provides communication with external devices in Master or Slave Mode. It also enables communication between processors if an external processor is connected to the system.

The Serial Peripheral Interface is essentially a shift register that serially transmits data bits to other SPIs. During a data transfer, one SPI system acts as the "master" which controls the data flow, while the other devices act as "slaves" which have data shifted into and out by the master.

A slave device is selected when the master asserts its NSS signal. If multiple slave devices exist, the master generates a separate slave select signal for each slave (NPCS). The SPI system consists of two data lines and two control lines:

Each SPI Controller has a dedicated receive and transmit DMA channel.

The Stamp9G20 has one SSC interface available, depending on the multiplexing of the pins.

The SSC supports many serial synchronous communication protocols generally used in audio and telecom applications such as I2S, Short Frame Sync, Long Frame Sync, etc.

The SSC has separated receive and transmit channels. Each channel has a data, a clock and a frame synchronization signal (RD, RK, RF, resp. TD, TK, TF). Both a receive and a transmit DMA channel are assigned to each SSC.

The Stamp9G20 has a maximum of 80 freely programmable digital I/O ports on its connectors. These pins are also used by other peripheral devices.

The Parallel Input/Output Controller(PIO) manages up to 32 programmable I/O ports. Each I/O port is associated with a bit number in the 32 bit register of the user interface. Each I/O port may be configured for general purpose I/O or assigned to a function of an integrated peripheral device. In doing so multiplexing with multiple integrated devices is possible. That means a pin may be used as GPIO or only as one of the peripheral functions. The PIO Controller also features a synchronous output providing up to 32 bits of data output in a single write operation.

The following characteristics are individually configurable for each PIO pin:

All configurations as well as the pin status can be read back by using the appropriate status register. Multiple pins of each PIO can also be written simultaneously by using the synchronous output register.

For interrupt handling, the PIO Controllers are considered as user peripherals. This means that the PIO Controller interrupt lines are connected among the interrupt sources 2 to 31. Refer to the PIO Controller peripheral identifier Table B.1, “Peripheral Identifiers” to identify the interrupt sources dedicated to the PIO Controllers. The PIO Controller interrupt can be generated only if the PIO Controller clock is enabled.

A number of the PIO signals might be used internally on the module. Care has to be taken when accessing the PIO registers in order not to change the settings of these internal signals, otherwise a system crash is likely to happen.

The Image Sensor Interface (ISI) supports direct connection to the ITU-R BT. 601/656 8-bit mode compliant sensors and up to 12-bit grayscale sensors. It receives the image data stream from the image sensor on the 12-bit data bus. This module receives up to 12 bits for data, the horizontal and vertical synchronizations and the pixel clock. The reduced pin count alternative for synchronization is supported for sensors that embed SAV (start of active video) and EAV (end of active video) delimiters in the data stream.

The Image Sensor Interface interrupt line is generally connected to the Advanced Interrupt Controller and can trigger an interrupt at the beginning of each frame and at the end of a DMA frame transfer. If the SAV/EAV synchronization is used, an interrupt can be triggered on each delimiter event.

For 8-bit color sensors, the data stream received can be in several possible formats: YCbCr 4:2:2, RGB 8:8:8, RGB 5:6:5 and may be processed before the storage in memory. The data stream may be sent on both preview path and codec path if the bit CODEC_ON in the ISI_CR1 is one. To optimize the bandwidth, the codec path should be enabled only when a capture is required.

In grayscale mode, the input data stream is stored in memory without any processing. The 12-bit data, which represent the grayscale level for the pixel, is stored in memory one or two pixels per word, depending on the GS_MODE bit in the ISI_CR2 register. The codec datapath is not available when grayscale image is selected.

The Stamp9G20 has a four ADC channels available.

The ADC is based on a Successive Approximation Register (SAR) 10-bit Analog-to-Digital Converter(ADC). It also integrates a 4-to-1 analog multiplexer, making possible the analog-to-digital conversions of 4 analog lines. The conversions extend from 0V to ADVREF.

The ADC supports an 8-bit or 10-bit resolution mode, and conversion results are reported in a common register for all channels, as well as in a channel-dedicated register. Software trigger, external trigger on rising edge of the ADTRG pin or internal triggers from Timer Counter output(s) are configurable.

The ADC also integrates a Sleep Mode and a conversion sequencer and connects with a DMA channel. These features reduce both power consumption and processor intervention.

Finally, the user can configure ADC timings, such as Startup Time and Sample and Hold Time.

The emac needs an aditional PHY design. The emac supports both, MII and RMII interface.

Please take care of the specific layout requirements of the Ethernet port when designing a base board. The two signals of the transmitter pair (ETX+ and ETX-) should be routed in parallel (constant distance, e.g. 0.5mm) with no vias on their way to the RJ45-jack. The same is true for the receiver pair (ERX+ and ERX-). No other signals should be crossing or get next to these lines. If a ground plane is used on the base board, it should be omitted in the vicinity of the Ethernet signals.

A 1nF / 2kV capacitor should be connected between board ground and chassis ground (which is usually connected to the shield of the RJ45-jack).

External Parts.  A few external parts are required for the proper operation of the UHP:

V_BUS considerations for USB Host.  A USB host port has to provide a supply voltage V_BUS of 5V +- 5% which has to be able to source a maximum of 500mA, or 100mA in case of battery operation. Please refer to the appropriate rules in the USB specification. A low ESR capacitor of at least 120µF has to be provided on V_BUS in order to avoid excessive voltage drops during current spikes.

V_BUS has to have an over-current protection. The over-current drawn temporarily on V_BUS must not exceed 5A. Polymeric PTCs or solid state switches are recommended by the specification. Suitable PPTCs are "MultiFuse" (Bourns), "PolyFuse" (Wickmann/Littelfuse), "PolySwitch" (Raychem/Tyco).

It is required that the over-current condition can be detected by software, so that V_BUS can be switched off or be reduced in power in such a case.

Layout considerations.  If external resistors are needed, they should be placed in the vicinity of the module's connector. The two traces of any of the differential pairs (USB-Host A+ and USB-Host A- , as well as USB-Host B+ and USB-Host B-) should not encircle large areas on the base board, in order to reduce signal distortion and noise. The are preferably routed closely in parallel to the USB connector.

USB High-Speed.  If designing USB High-Speed a wave impedance of 90 Ω on the traces should be respected. The traces shoud be routed as short as possible and in parallel with as low parallel capacitance as possible.

External Parts.  A few external parts are required for the proper operation of the UDP:

The USB specification demands a switchable pull-up resistor of 1.5 kΩ on USB-Device+ which identifies the UDP as a full speed device to the attached host controller. On this module, this resistor is integrated on the chip. It can be switched on or off using the "USB Pad Pull-up Control Register", which is part of the "Bus Matrix User Interface" (not the "USB Device Port User Interface", as one might expect). This pull-up resistor is required to be switchable in order not to source current to an attached but powered down host. This would otherwise constitute an irregular condition on the host. The software has to take care of this fact.

The capacitors are intended to improve the signal quality (edge rate control) depending on the specific design. They are not mandatory. The total capacitance to ground of each USB pin, the PCB trace to the series resistor, and the capacitor must not exceed 75pF.

Operation with V_BUS as a Supply.  Special care has to be taken if the module is powered by the VBUS supply. Please refer to the appropriate rules in the USB specification with regard to inrush current limiting and power switching. As the module draws more than 100mA in normal mode, it is a "high-power" device according to the specification (<100mA = "low-power", 100..500mA = "high-power"). It therefore requires staged switching which means that at power-up it should draw not more than 100mA on VBUS. The capacitive load of a USB device on VBUS should be not higher than 10µF.

Layout considerations.  The external resistors should be placed in the vicinity of the module's connector. The traces of the differential pair (USB-Device+ and USB-Device- ) should not encircle large areas on the base board, in order to reduce signal distortion and noise. The are preferably routed closely in parallel to the USB connector.

On the Stamp9G20 the memory bus is driven with 1.8V. This affects the voltages of PIOC-controller pins, they are 1.8V as well. Not affected are the ADC-Channels, which have their own ADV_REF. The V_MEM pins on the module are pin one and two of the bus interface. If pins of PIOC or the memory bus are in use on the customer's design it is highly recommended to implement buffers on both memory bus and PIOC pins.

The memory bus is used inside of the module. It can be either 1.8V or 3.3V. The V_mem pin of the module is powered by the module itself. Do not power this pin externally to maintain inter-product dependencies. A difference between V_mem and VCC may also affect the behaviour of one PIO-controller of the respective module.

To connect 3.3V chips to the memory bus or to maintain compatibility between various products it is recommended to implement buffer chips on the memory bus externally, like shown in Figure 5.1, “Buffered Memory Bus (PIOC) 1.8V - 3.3V”

To connect 5V chips the same schematics can be used with suitable buffer chips.

Figure 5.1. Buffered Memory Bus (PIOC) 1.8V - 3.3V

The Stamp9G20 Starterkit contains the following components:

The Panel-Card EVB (Evaluation Board) is designed to be both simple and universal. Some elements of the circuit board will not always be needed, but facilitate implementation for certain purposes. It was designed to serve the Panel-Card and other products as an evaluation platform.

2.7. Schematics

The following circuit diagram is intended for reference only and does not dispense the user from checking and applying the appropriate standards. No warranty can be granted if parts of the circuit are used in customer applications.

Figure 6.1. Panel-Card EVB Schematics Bus/JTAG

Figure 6.2. Panel-Card EVB Schematics USB/RS232

Figure 6.3. Panel-Card EVB Schematics Power Regulation

Figure 6.4. Panel-Card EVB Schematics Connectors

Figure 6.5. Panel-Card EVB Schematics HID