
654
6222H–ATARM–25-Jan-12
SAM7SE512/256/32
43.2.3
Pulse Width Modulation Controller (PWM)
43.2.3.1
PWM: Update when PWM_CCNTx = 0 or 1
If the Channel Counter Register value is 0 or 1, the Channel Period Register or Channel Duty
Cycle Register is directly modified when writing the Channel Update Register.
Problem Fix/Workaround
Check the Channel Counter Register before writing the Channel Update Register.
43.2.3.2
PWM: Update when PWM_CPRDx = 0
When the Channel Period Register equals 0, the period update is not operational.
Problem Fix/Workaround
Do not write 0 in the Channel Period Register.
43.2.3.3
PWM: Counter Start Value
In left aligned mode, the first start value of the counter is 0. For the other periods, the counter
starts at 1.
Problem Fix/Workaround
None.
43.2.3.4
PWM: Behavior of CHIDx Status Bits in the PWM_SR Register
There is an erratic behavior of the CHIDx status bit in the PWM_SR Register. When a channel is
disabled by writing in the PWM_DIS Register just after enabling it (before completion of a Clock
Period of the clock selected for the channel), the PWM line is internally disabled but the CHIDx
status bit in the PWM_SR stays at 1.
Problem Fix/Workaround
Do not disable a channel before completion of one period of the selected clock.
43.2.4
Real-Time Timer (RTT)
43.2.4.1
RTT: Possible Event Loss when Reading RTT_SR
If an event (RTTINC or ALMS) occurs within the same slow clock cycle when RTT_SR is read,
the corresponding bit might be cleared. This might lead to the loss of this event.
Problem Fix/Workaround
The software must handle RTT event as interrupt and should not poll RTT_SR.
43.2.5
SDRAM Controller (SDRAMC)
43.2.5.1
SDRAMC: PDC Buffer in 16-bit SDRAM while the Core Accesses SDRAM
When the SAM7SE interfaces with 16-bit SDRAM memory and the processor accesses the
SDRAM, either for instruction fetch or data read/write, the data transferred by the PDC from
SDRAM buffers to the peripherals might be corrupted. Transfers from peripherals to SDRAM
buffers are not affected.
Problem Fix/Workaround
Map the transmit PDC buffers in internal SRAM or Flash.