AT91SAM7X128 Atmel, AT91SAM7X128 Datasheet - Page 564

• Manufacturer Part Number: AT91SAM7X128
• Description: MCU 32-Bit 91S ARM7TDMI RISC 128KB Flash 1.8V/3.3V 100-Pin LQFP
• Manufacturer: Atmel

Specifications of AT91SAM7X128

• Package: 100LQFP
• Device Core: ARM7TDMI
• Family Name: 91S
• Maximum Speed: 55 MHz
• Ram Size: 32 KB
• Program Memory Size: 128 KB
• Operating Supply Voltage: 1.8|3.3 V
• Data Bus Width: 32 Bit
• Program Memory Type: Flash
• Number Of Programmable I/os: 62
• Interface Type: CAN/Ethernet/SPI/I2S/TWI/USART/USB
• On-chip Adc: 8-chx10-bit
• Operating Temperature: -40 to 85 °C
• Number Of Timers: 3

37.3
37.3.1
564
Functional Description
AT91SAM7X512/256/128 Preliminary
Memory Interface
The EMAC has several clock domains:
The only system constraint is 160 MHz for the system bus clock, above which MDC would toggle
at above 2.5 MHz.
The system bus clock must run at least as fast as the receive clock and transmit clock (25 MHz
at 100 Mbps, and 2.5 MHz at 10 Mbps).
The control registers drive the MDIO interface, setup up DMA activity, start frame transmission
and select modes of operation such as full- or half-duplex.
The receive block checks for valid preamble, FCS, alignment and length, and presents received
frames to the address checking block and DMA interface.
The transmit block takes data from the DMA interface, adds preamble and, if necessary, pad
and FCS, and transmits data according to the CSMA/CD (carrier sense multiple access with col-
lision detect) protocol. The start of transmission is deferred if CRS (carrier sense) is active.
If COL (collision) becomes active during transmission, a jam sequence is asserted and the
transmission is retried after a random back off. CRS and COL have no effect in full duplex mode.
The DMA block connects to external memory through its ASB bus interface. It contains receive
and transmit FIFOs for buffering frame data. It loads the transmit FIFO and empties the receive
FIFO using ASB bus master operations. Receive data is not sent to memory until the address
checking logic has determined that the frame should be copied. Receive or transmit frames are
stored in one or more buffers. Receive buffers have a fixed length of 128 bytes. Transmit buffers
range in length between 0 and 2047 bytes, and up to 128 buffers are permitted per frame. The
DMA block manages the transmit and receive framebuffer queues. These queues can hold mul-
tiple frames.
Frame data is transferred to and from the EMAC through the DMA interface. All transfers are 32-
bit words and may be single accesses or bursts of 2, 3 or 4 words. Burst accesses do not cross
sixteen-byte boundaries. Bursts of 4 words are the default data transfer; single accesses or
bursts of less than four words may be used to transfer data at the beginning or the end of a
buffer.
The DMA controller performs six types of operation on the bus. In order of priority, these are:
Figure 37-1
•
•
•
1. Receive buffer manager write
2. Receive buffer manager read
3. Transmit data DMA read
4. Receive data DMA write
5. Transmit buffer manager read
6. Transmit buffer manager write
System bus clock (AHB and APB): DMA and register blocks
Transmit clock: transmit block
Receive clock: receive and address checker blocks
illustrates the different blocks of the EMAC module.
6120H–ATARM–17-Feb-09