AT91SAM7S256D-AU Atmel, AT91SAM7S256D-AU Datasheet - Page 82
AT91SAM7S256D-AU
Manufacturer Part Number
AT91SAM7S256D-AU
Description
ARM Microcontrollers - MCU 256K Flash SRAM 64K ARM based MCU
Manufacturer
Atmel
Series
SAM7S256r
Datasheet
1.AT91SAM7S256D-AU.pdf
(775 pages)
Specifications of AT91SAM7S256D-AU
Rohs
yes
Core
ARM
Processor Series
AT91SAM
Data Bus Width
16 bit/32 bit
Maximum Clock Frequency
55 MHz
Program Memory Size
256 KB
Data Ram Size
64 KB
On-chip Adc
Yes
Operating Supply Voltage
3 V to 3.6 V
Operating Temperature Range
- 40 C to + 85 C
Package / Case
LQFP-64
Mounting Style
SMD/SMT
Interface Type
2-Wire, I2S, SPI, USART
Length
7 mm
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15.3
Figure 15-2. Enabling/Disabling PIT with PITEN
MCK Prescaler
Functional Description
The Periodic Interval Timer aims at providing periodic interrupts for use by operating systems.
The PIT provides a programmable overflow counter and a reset-on-read feature. It is built around two counters: a
20-bit CPIV counter and a 12-bit PICNT counter. Both counters work at Master Clock /16.
The first 20-bit CPIV counter increments from 0 up to a programmable overflow value set in the field PIV of the
Mode Register (PIT_MR). When the counter CPIV reaches this value, it resets to 0 and increments the Periodic
Interval Counter, PICNT. The status bit PITS in the Status Register (PIT_SR) rises and triggers an interrupt, pro-
vided the interrupt is enabled (PITIEN in PIT_MR).
Writing a new PIV value in PIT_MR does not reset/restart the counters.
When CPIV and PICNT values are obtained by reading the Periodic Interval Value Register (PIT_PIVR), the over-
flow counter (PICNT) is reset and the PITS is cleared, thus acknowledging the interrupt. The value of PICNT gives
the number of periodic intervals elapsed since the last read of PIT_PIVR.
When CPIV and PICNT values are obtained by reading the Periodic Interval Image Register (PIT_PIIR), there is no
effect on the counters CPIV and PICNT, nor on the bit PITS. For example, a profiler can read PIT_PIIR without
clearing any pending interrupt, whereas a timer interrupt clears the interrupt by reading PIT_PIVR.
The PIT may be enabled/disabled using the PITEN bit in the PIT_MR register (disabled on reset). The PITEN bit
only becomes effective when the CPIV value is 0.
is reset (PITEN= 0), the CPIV goes on counting until the PIV value is reached, and is then reset. PIT restarts count-
ing, only if the PITEN is set again.
The PIT is stopped when the core enters debug state.
PITS (PIT_SR)
APB Interface
PICNT
PITEN
CPIV
15
0
0
1
0
PIV - 1
PIV
Figure 15-2
MCK
read PIT_PIVR
1
APB cycle
illustrates the PIT counting. After the PIT Enable bit
0
SAM7S Series [DATASHEET]
APB cycle
0
restarts MCK Prescaler
6175M–ATARM–26-Oct-12
1
82
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