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ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
The Stop condition provides a Timer Enable/Disable function.
12.3.2 GTCCR – General Timer/Counter1 Control Register
• Bit 6 – PWM1B: Pulse Width Modulator B Enable
When set (one) this bit enables PWM mode based on comparator OCR1B in Timer/Counter1 and the counter
value is reset to $00 in the CPU clock cycle after a compare match with OCR1C register value.
• Bits 5:4 – COM1B[1:0]: Comparator B Output Mode, Bits 1 and 0
The COM1B1 and COM1B0 control bits determine any output pin action following a compare match with compare
register B in Timer/Counter1. Since the output pin action is an alternative function to an I/O port, the corresponding
direction control bit must be set (one) in order to control an output pin.
In Normal mode, the COM1B1 and COM1B0 control bits determine the output pin actions that affect pin PB4
(OC1B) as described in Table 12-6. Note that OC1B
is not connected in normal mode.
In PWM mode, these bits have different functions. Refer to Table 12-1 on page 86 for a detailed description.
• Bit 3 – FOC1B: Force Output Compare Match 1B
Writing a logical one to this bit forces a change in the compare match output pin PB4 (OC1B) according to the val-
ues already set in COM1B1 and COM1B0. If COM1B1 and COM1B0 written in the same cycle as FOC1B, the new
settings will be used. The Force Output Compare bit can be used to change the output pin value regardless of the
timer value. The automatic action programmed in COM1B1 and COM1B0 takes place as if a compare match had
0 1 1 1 PCK/64 CK/64
1 0 0 0 PCK/128 CK/128
1 0 0 1 PCK/256 CK/256
1 0 1 0 PCK/512 CK/512
1 0 1 1 PCK/1024 CK/1024
1 1 0 0 PCK/2048 CK/2048
1 1 0 1 PCK/4096 CK/4096
1 1 1 0 PCK/8192 CK/8192
1 1 1 1 PCK/16384 CK/16384
Table 12-5. Timer/Counter1 Prescale Select (Continued)
CS13 CS12 CS11 CS10
Asynchronous
Clocking Mode
Synchronous
Clocking Mode
Bit 7 6 5 4 3 2 1 0
0x2C
TSM PWM1B COM1B1 COM1B0 FOC1B FOC1A PSR1 PSR0 GTCCR
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial value 0 0 0 0 0 0 0 0
Table 12-6. Comparator B Mode Select in Normal Mode
COM1B1 COM1B0 Description
0 0 Timer/Counter Comparator B disconnected from output pin OC1B.
0 1 Toggle the OC1B output line.
1 0 Clear the OC1B output line.
1 1 Set the OC1B output line