Z86L972 Datasheet, PDF (53/91 Pages) Zilog, Inc. – Low-Voltage Microcontrollers

Z86L972/Z86L973/Z86L974
Low-Voltage Microcontrollers
46
T16 Transit Mode
In normal or ping-pong mode, the output of T16, when not enabled, is dependent
on CTR1, D0. If CTR1, D0 is a 0, T16_OUT is a 1; if CTR1, D0 is a 1, T16_OUT is
0. You can force the output of T16 to either a 0 or 1, whether it is enabled or not,
by programming CTR1 D3, D2 to a 10 or 11.
When T16 is enabled, TC16H * 256 + TC16L is loaded, and T16_OUT is switched
to its initial value (CTR1 d0). When T16 counts down to 0, T16_OUT is toggled (in
normal or ping-pong mode), an interrupt is generated if enabled (CTR2 D1), and a
status bit (CTR2 D5) is set. If it is in modulo-N mode, it is loaded with TC16H * 256
+ TC16L, and the counting continues.
You can modify the values in TC16H and TC16L at any time. The new values take
effect when they are loaded. Do not load these registers at the time the values are
to be loaded into the counter/timer. An initial count of 1 is not allowed. An initial
count of 0 causes T16 to count from 0 to FFFFh to FFFEh. Transition from 0 to
FFFFh is not a time-out condition.
T16 Demodulation Mode
Program TC16L and TC16H to FFh. After T16 is enabled, when the first edge (ris-
ing, falling, or both, depending on CTR1 D5, D4) is detected, T16 captures HI16
and LO16, reloads, and begins counting.
Ping-Pong Mode
This operation mode is only valid in transmit mode. T8 and T16 must be pro-
grammed in single-pass mode (CTR0 D6, CTR2 D6), and ping-pong mode must
be programmed in CTR1 D3, D2. You can begin the operation by enabling either
T8 or T16 (CTR0 D7 or CTR2 D7). For example, if T8 is enabled, T8_OUT is set
to this initial value (CTR1 D1). According to T8_OUT’s level, TC8H or TC8L is
loaded into T8. After the terminal count is reached, T8 is disabled, and T16 is
enabled. T16_OUT switches to its initial value (CTR1 D0), data from TC16H and
TC16L is loaded, and T16 starts to count. After T16 reaches the terminal count, it
stops. T8 is enabled again, and the whole cycle repeats. Interrupts can be allowed
when T8 or T16 reaches terminal control (CTR0 D1, CTR2 D1). To stop the ping-
pong operation, write 00 to bits D3 and D2 or CTR1.
Note: Enabling ping-pong operation while the counters/timers are
running can cause intermittent counter/timer function. Disable
the counters/timers, then reset the status flags before starting
the ping-pong mode.
PS010504-1002
PRELIMINARY