Z86L79 Datasheet, PDF (30/58 Pages) Zilog, Inc. – Low-Voltage Microcontroller

Z86L79/80
Low-Voltage Microcontroller
Zilog
FUNCTIONAL DESCRIPTION (Continued)
Input Circuit
The edge detector monitors the input signal on P31 or P20.
Based on CTR1 D5-D4, a pulse is generated at the Pos
Edge or Neg Edge line when an edge is detected. Glitches
in the input signal which have a width less than specified
(CTR1 D3, D2) are filtered out.
T8 Transmit Mode
When T8 is enabled, the output of T8 depends on CTR1,
D1. If it is 0, T8_OUT is 1. If it is 1, T8_OUT is 0.
When T8 is enabled, the output T8_OUT switches to the
initial value (CTR1 D1). If the initial value (CTR1 D1) is 0,
TC8L is loaded, otherwise TC8H is loaded into the
counter. In Single-Pass Mode (CTR0 D6), T8 counts down
to 0 and stops, T8_OUT toggles, the time-out status bit
(CTR0 D5) is set, and a time-out interrupt can be generat-
ed if it is enabled (CTR0 D1) (Figure 22). In Modulo-N
Mode, upon reaching terminal count, T8_OUT is toggled,
but no interrupt is generated. Then T8 loads a new count
(if the T8_OUT level now is 0), TC8L is loaded; if it is 1,
TC8H is loaded. T8 counts down to 0, toggles T8_OUT,
sets the time-out status bit (CTR0 D5) and generates an
interrupt if enabled (CTR0 D1) (Figure 23). This completes
one cycle. T8 then loads from TC8H or TC8L according to
the T8_OUT level, and repeats the cycle.
The user can modify the values in TC8H or TC8L at any
time. The new values take effect when they are loaded.
Care must be taken not to write these registers at the time
the values are to be loaded into the counter/timer, to en-
sure known operation. An initial count of 1 is not allowed (a
non-function will occur). An initial count of 0 will cause TC8
to count from 0 to %FF to %FE (Note, % is used for hexa-
decimal values). Transition from 0 to %FF is not a time-out
condition.
Note: Using the same instructions for stopping the
counter/timers and setting the status bits is not recom-
mended. Two successive commands, first stopping the
counter/timers, then resetting the status bits is necessary.
This is required because it takes one counter/timer clock
interval for the initiated event to actually occur.
TC8H Counts
T8_OUT
“Counter Enable” Command,
T8_OUT Switches To Its
Initial Value (CTR1 D1)
T8_OUT Toggles,
Time-Out Interrupt
Figure 20. T8_OUT in Single-Pass Mode
T8_OUT Toggles
TC8L
TC8H
TC8L
TC8H
TC8L
“Counter Enable” Command,
T8_OUT Switches To Its
Initial Value (CTR1 D1)
Time-Out Interrupt
Time-Out Interrupt
Figure 21. T8_OUT in Modulo-N Mode
3-30
PRELIMINARY
DS97LVO0601