AT91SAM7S256C-MU Atmel, AT91SAM7S256C-MU Datasheet - Page 153

• Manufacturer Part Number: AT91SAM7S256C-MU
• Description: IC ARM7 MCU 32BIT 256K 64-QFN
• Manufacturer: Atmel
• Series: AT91SAMr

Specifications of AT91SAM7S256C-MU

• Core Processor: ARM7
• Core Size: 16/32-Bit
• Speed: 55MHz
• Connectivity: I²C, SPI, SSC, UART/USART, USB
• Peripherals: Brown-out Detect/Reset, DMA, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 256KB (256K x 8)
• Program Memory Type: FLASH
• Ram Size: 64K x 8
• Voltage - Supply (vcc/vdd): 1.65 V ~ 1.95 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-VQFN Exposed Pad, 64-HVQFN, 64-SQFN, 64-DHVQFN
• Processor Series: AT91
• Core: ARM7TDMI
• Data Bus Width: 32 bit
• Data Ram Size: 64 KB
• Interface Type: SPI, TWI, USART, USB
• Maximum Clock Frequency: 55 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 5
• Operating Supply Voltage: 3.3 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Operating Temperature Range: - 40 C to + 85 C
• For Use With: AT91SAM-ICE - EMULATOR FOR AT91 ARM7/ARM9AT91SAM7S-EK - KIT EVAL FOR ARM AT91SAM7S
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Lead Free Status / Rohs Status: Details
• Other names: AT91SAM7S256-MU; AT91SAM7S256-MU

22.3.4
22.3.5
6175K–ATARM–30-Aug-10
Data Transfers
Priority of PDC Transfer Requests
Programming the Next Counter/Pointer registers chains the buffers. The counters are decre-
mented after each data transfer as stated above, but when the transfer counter reaches zero,
the values of the Next Counter/Pointer are loaded into the Counter/Pointer registers in order to
re-enable the triggers.
For each channel, two status bits indicate the end of the current buffer (ENDRX, ENDTX) and
the end of both current and next buffer (RXBUFF, TXBUFE). These bits are directly mapped to
the peripheral status register and can trigger an interrupt request to the AIC.
The peripheral end flag is automatically cleared when one of the counter-registers (Counter or
Next Counter Register) is written.
Note: When the Next Counter Register is loaded into the Counter Register, it is set to zero.
The peripheral triggers PDC transfers using transmit (TXRDY) and receive (RXRDY) signals.
When the peripheral receives an external character, it sends a Receive Ready signal to the PDC
which then requests access to the system bus. When access is granted, the PDC starts a read
of the peripheral Receive Holding Register (RHR) and then triggers a write in the memory.
After each transfer, the relevant PDC memory pointer is incremented and the number of trans-
fers left is decremented. When the memory block size is reached, a signal is sent to the
peripheral and the transfer stops.
The same procedure is followed, in reverse, for transmit transfers.
The Peripheral DMA Controller handles transfer requests from the channel according to priori-
ties fixed for each product.These priorities are defined in the product datasheet.
If simultaneous requests of the same type (receiver or transmitter) occur on identical peripher-
als, the priority is determined by the numbering of the peripherals.
If transfer requests are not simultaneous, they are treated in the order they occurred. Requests
from the receivers are handled first and then followed by transmitter requests.
AT91SAM7S Series Preliminary
153