121
2588B–AVR–11/06
ATtiny261/461/861
the Output Compare Override Enable Bit is cleared. Table 16-20 shows the Output Compare
Override Enable Bits and their corresponding Output Compare pins.
16.11.6 TCNT1 – Timer/Counter1
This 8-bit register contains the value of Timer/Counter1.
The Timer/Counter1 is realized as a 10-bit up/down counter with read and write access. Due to
synchronization of the CPU, Timer/Counter1 data written into Timer/Counter1 is delayed by one
and half CPU clock cycles in synchronous mode and at most one CPU clock cycles for asyn-
chronous mode. When a 10-bit accuracy is preferred, special procedures must be followed for
accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures are
described in section ”Accessing 10-Bit Registers” on page 110. Alternatively the Timer/Counter1
can be used as an 8-bit Timer/Counter. Note that the Timer/Counter1 always starts counting up
after writing the TCNT1 register.
16.11.7 TC1H – Timer/Counter1 High Byte
The temporary Timer/Counter1 register is an 2-bit read/write register.
• Bits 7:2 - Res: Reserved Bits
These bits are reserved bits in the ATtiny261/461/861 and always reads as zero.
• Bits 1:0 - TC19, TC18: Two MSB bits of the 10-bit accesses
If 10-bit accuracy is used, the Timer/Counter1 High Byte Register (TC1H) is used for temporary
storing the MSB bits (TC19, TC18) of the 10-bit acceses. The same TC1H register is shared
between all 10-bit registers within the Timer/Counter1. Note that special procedures must be fol-
lowed when accessing the 10-bit TCNT1 register via the 8-bit AVR data bus. These procedures
are described in section ”Accessing 10-Bit Registers” on page 110.
16.11.8 OCR1A – Timer/Counter1 Output Compare Register A
The output compare register A is an 8-bit read/write register.
Table 16-20. Output Compare Override Enable Bits vs. Output Compare Pins
OC1OE0 OC1OE1 OC1OE2 OC1OE3 OC1OE4 OC1OE5
OC1A
(PB0) OC1A (PB1) OC1B (PB2) OC1B (PB3) OC1D (PB4) OC1D (PB5)
Bit 76543210
0x2E (0x4E) MSB LSB TCNT1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
Bit 76543210
0x25 (0x45) ------TC19TC18TC1H
Read/WriteRRRRRRR/WR/W
Initial value00000000
Bit 76543210
0x2D (0x4D) MSB LSB OCR1A
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value00000000
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