AT91SAM7X128 Atmel, AT91SAM7X128 Datasheet - Page 142

• 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

22.3
22.3.1
22.3.2
22.3.3
142
Functional Description
AT91SAM7X512/256/128 Preliminary
Configuration
Memory Pointers
Transfer Counters
The PDC channels user interface enables the user to configure and control the data transfers for
each channel. The user interface of a PDC channel is integrated into the user interface of the
peripheral (offset 0x100), which it is related to.
Per peripheral, it contains four 32-bit Pointer Registers (RPR, RNPR, TPR, and TNPR) and four
16-bit Counter Registers (RCR, RNCR, TCR, and TNCR).
The size of the buffer (number of transfers) is configured in an internal 16-bit transfer counter
register, and it is possible, at any moment, to read the number of transfers left for each channel.
The memory base address is configured in a 32-bit memory pointer by defining the location of
the first address to access in the memory. It is possible, at any moment, to read the location in
memory of the next transfer and the number of remaining transfers. The PDC has dedicated sta-
tus registers which indicate if the transfer is enabled or disabled for each channel. The status for
each channel is located in the peripheral status register. Transfers can be enabled and/or dis-
abled by setting TXTEN/TXTDIS and RXTEN/RXTDIS in PDC Transfer Control Register. These
control bits enable reading the pointer and counter registers safely without any risk of their
changing between both reads.
The PDC sends status flags to the peripheral visible in its status-register (ENDRX, ENDTX,
RXBUFF, and TXBUFE).
ENDRX flag is set when the PERIPH_RCR register reaches zero.
RXBUFF flag is set when both PERIPH_RCR and PERIPH_RNCR reach zero.
ENDTX flag is set when the PERIPH_TCR register reaches zero.
TXBUFE flag is set when both PERIPH_TCR and PERIPH_TNCR reach zero.
These status flags are described in the peripheral status register.
Each peripheral is connected to the PDC by a receiver data channel and a transmitter data
channel. Each channel has an internal 32-bit memory pointer. Each memory pointer points to a
location anywhere in the memory space (on-chip memory or external bus interface memory).
Depending on the type of transfer (byte, half-word or word), the memory pointer is incremented
by 1, 2 or 4, respectively for peripheral transfers.
If a memory pointer is reprogrammed while the PDC is in operation, the transfer address is
changed, and the PDC performs transfers using the new address.
There is one internal 16-bit transfer counter for each channel used to count the size of the block
already transferred by its associated channel. These counters are decremented after each data
transfer. When the counter reaches zero, the transfer is complete and the PDC stops transfer-
ring data.
If the Next Counter Register is equal to zero, the PDC disables the trigger while activating the
related peripheral end flag.
If the counter is reprogrammed while the PDC is operating, the number of transfers is updated
and the PDC counts transfers from the new value.
6120H–ATARM–17-Feb-09