C515 Datasheet, PDF (29/55 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C515
Compare Mode 1
If compare mode 1 is enabled and the software writes to the appropriate output latch at the port, the
new value will not appear at the output pin until the next compare match occurs. Thus, it can be
chosen whether the output signal has to make a new transition (1-to-0 or 0-to-1, depending on the
actual pin-level) or should keep its old value at the time when the timer value matches the stored
compare value.
In compare mode 1 (see figure 12) the port circuit consists of two separate latches. One latch
(which acts as a "shadow latch") can be written under software control, but its value will only be
transferred to the port latch (and thus to the port pin) when a compare match occurs.
Port Circuit
Compare Register
Circuit
Compare Reg.
16 Bit
Comparator
16 Bit
Timer Register
Timer Circuit
Compare
Match
Internal
Bus
Write to
Latch
Read Latch
V_CC
D
Q
D
Q
Port
Shadow
Port
Pin
Latch
Latch
CLK
CLK
Q
Read Pin
MCS02662
Figure 12
Compare Function in Compare Mode 1
Semiconductor Group
29
1997-08-01