Rainbow Electronics ATtiny15L - Manual (Page 26)

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ATtiny15L
1187E–AVR–06/02
The Special Function IO
Register – SFIOR
• Bit 7..3 – Res: Reserved Bits
These bits are reserved bits in the ATtiny15L and always read as zero.
• Bit 2 – FOC1A: Force Output Compare 1A
Writing a logical “1” to this bit forces a change in the Compare Match Output pin PB1
(OC1A) according to the values already set in COM1A1 and COM1A0. The Force Out-
put Compare bit can be used to change the output pin without waiting for a compare
match in timer. The automatic action programmed in COM1A1 and COM1A0 happens
a s if a Co mp are M a tch had occurre d, bu t n o in te rrupt i s gen erated and th e
Timer/Counter1 will not be cleared even if CTC1 is set. The FOC1A bit will always be
read as zero. The setting of the FOC1A bit has no effect in PWM mode.
• Bit 1 – PSR1: Prescaler Reset Timer/Counter1
When this bit is set (one) the Timer/Counter1 prescaler will be reset. The bit will be
cleared by hardware after the operation is performed. Writing a “0” to this bit will have no
effect. This bit will always be read as zero.
• Bit 0 – PSR0: Prescaler Reset Timer/Counter0
When this bit is set (one) the Timer/Counter0 prescaler will be reset. The bit will be
cleared by hardware after the operation is performed. Writing a “0” to this bit will have no
effect. This bit will always be read as zero.
The 8-bit Timer/Counter0 Figure 20 shows the block diagram for Timer/Counter0.
The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK or an external
p in . In a dd i tio n, i t can b e sto pp ed as de scri be d i n the spe ci fica tio n fo r th e
Timer/Counter0 Control Register (TCCR0). The Overflow Status Flag is found in the
Timer/Counter Interrupt Flag Register (TIFR). Control signals are found in the
Timer/Counter0 Control Register (TCCR0). The interrupt enable/disable settings for
Timer/Counter0 are found in the Timer/Counter Interrupt Mask Register (TIMSK).
When Timer/Counter0 is externally clocked, the external signal is synchronized with the
oscillator frequency of the CPU. To ensure proper sampling of the external clock, the
minimum time between two external clock transitions must be at least one internal CPU
clock period. The external clock signal is sampled on the rising edge of the internal CPU
clock.
The 8-bit Timer/Counter0 features both a high-resolution and a high-accuracy usage
with the lower prescaling opportunities. Similarly, the high-prescaling opportunities
make the Timer/Counter0 useful for lower-speed functions or exact-timing functions with
infrequent actions.
Bit 7 6 5 4 3 2 1 0
$2C – – – – – FOC1A PSR1 PSR0 SFIOR
Read/Write R R R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0