AT94K05AL ATMEL Corporation, AT94K05AL Datasheet - Page 101

• Manufacturer Part Number: AT94K05AL
• Description: Fpslic Devices Combine 5K Gates of Atmel's Patented AT40K Fpga Architecture, a 20 Mips Avr 8-bit Risc Microprocessor Core, Numerous Fixed Microcontroller Peripheries And up to 36K Bytes of Program And Data SRAM.
• Manufacturer: ATMEL Corporation

Timer/Counter1 in
PWM Mode
Rev. 1138F–FPSLI–06/02
Timer/Counter1 Input Capture Register – ICR1H AND ICR1L
The input capture register is a 16-bit read-only register.
When the rising or falling edge (according to the input capture edge setting – ICES1) of the
signal a t the input capture pin – PE7(ICP) – is detected , the current value of the
Timer/Counter1 Register – TCNT1 is transferred to the Input Capture Register – ICR1. In the
same cycle, the input capture flag – ICF1 – is set (one).
Since the Input Capture Register – ICR1 – is a 16-bit register, a temporary register TEMP is
used when ICR1 is read to ensure that both bytes are read simultaneously. When the CPU
reads the low byte ICR1L, the data is sent to the CPU and the data of the high byte ICR1H is
placed in the TEMP register. When the CPU reads the data in the high byte ICR1H, the CPU
receives the data in the TEMP register. Consequently, the low byte ICR1L must be accessed
first for a full 16-bit register read operation.
The TEMP register is also used when accessing TCNT1, OCR1A and OCR1B. If the main pro-
gram and also interrupt routines perform access to registers using TEMP, interrupts must be
disabled during access from the main program and interrupt routine.
When the PWM mode is selected, Timer/Counter1 and the Output Compare Register1A –
OCR1A and the Output Compare Register1B – OCR1B, form a dual 8-, 9- or 10-bit, free-run-
ning, glitch-free and phase correct PWM with outputs on the PD6(OC1A) and PE5(OC1B)
pins. In this mode the Timer/Counter1 acts as an up/down counter, counting up from $0000 to
TOP (see Table 29), where it turns and counts down again to zero before the cycle is
repeated. When the counter value matches the contents of the 8, 9 or 10 least significant bits
(depends of the resolution) of OCR1A or OCR1B, the PD6(OC1A)/PE5(OC1B) pins are set or
cleared according to the settings of the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the
Timer/Counter1 Control Register TCCR1A. Refer to Table 30 for details.
Alternatively, the Timer/Counter1 can be configured to a PWM that operates at twice the
speed as in the mode described above. Then the Timer/Counter1 and the Output Compare
Register1A – OCR1A and the Output Compare Register1B – OCR1B, form a dual 8-, 9- or 10-
bit, free-running and glitch-free PWM with outputs on the PE6(OC1A) and PE5(OC1B) pins.
As shown in Table 29, the PWM operates at either 8-, 9- or 10-bit resolution. Note the unused
bits in OCR1A, OCR1B and TCNT1 will automatically be written to zero by the hardware. For
example, bit 9 to 15 will be set to zero in OCR1A, OCR1B and TCNT1 if the 9-bit PWM resolu-
tion is selected. This makes it possible for the user to perform read-modify-write operations in
any of the three resolution modes and the unused bits will be treated as “don’t care”.
Bit
$25 ($45)
$24 ($44)
Read/Write
Initial Value
15
MSB
7
R
R
0
0
14
6
R
R
0
0
13
5
R
R
0
0
12
4
R
R
0
0
11
3
R
R
0
0
AT94K Series FPSLIC
10
2
R
R
0
0
9
1
R
R
0
0
8
LSB
0
R
R
0
0
ICR1H
ICR1L
101