AT90S/LS4434 and AT90S/LS8535
39
Figure 33.
Effects of Unsynchronized OCR1 Latching
During the time between the write and the latch operations, a read from OCR1A or OCR1B will read the contents of the
temporary location. This means that the most recently written value always will read out of OCR1A/B.
When the OCR1A/OCR1B contains $0000 or TOP, the output OC1A/OC1B is updated to low or high on the next compare
match according to the settings of COM1A1/COM1A0 or COM1B1/COM1B0. This is shown in Table 17.
Note:
X = A
In PWM mode, the Timer Overflow Flag1 (TOV1) is set when the counter advances from $0000. Timer Overflow Interrupt1
operates exactly as in normal Timer/Counter mode, i.e., it is executed when TOV1 is set, provided that Timer Overflow
Interrupt1 and global interrupts are enabled. This also applies to the Timer Output Compare1 flags and interrupts.
Table 17.
PWM Outputs OCR1X = $0000 or TOP
COM1X1
COM1X0
OCR1X
Output OC1X
1
0
$0000
L
1
0
TOP
H
1
1
$0000
H
1
1
TOP
L
Counter Value
Compare Value
PWM Output OC1X
Synchronized
OCR1X Latch
Counter Value
Compare Value
PWM Output OC1X
Unsynchronized
OCR1X Latch
Glitch
Compare Value changes
Note: X = A or B
Compare Value changes