Z86L79 Datasheet, PDF (34/58 Pages) Zilog, Inc. – Low-Voltage Microcontroller

Z86L79/80
Low-Voltage Microcontroller
FUNCTIONAL DESCRIPTION (Continued)
Z8 Data Bus
Pos Edge
Neg Edge
HI8
CTR0 D4, D3
SCLK
Clock
Select
Clock
8-Bit
Counter T8
CTR0 D2
LO8
Zilog
IRQ4
CTR0 D1
T8_OUT
Z8 Data Bus
TC8H
TC8L
Figure 25. 16-Bit Counter/TImer Circuits
T16 Transmit Mode
In Normal or Ping-Pong Mode, the output of T16 when not
enabled is dependent on CTR1, D0. If it is a 0, T16_OUT
is a 1; if it is a 1, T16_OUT is 0. The user can force the out-
put 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 Nor-
mal or Ping-Pong Mode), an interrupt is generated if en-
abled (CTR2 D1), and a status bit (CTR2 D5) is set. Note
that global interrupts will override this function as de-
scribed in the interrupts section. If T16 is in Single-Pass
Mode, it is stopped at this point. If it is in Modulo-N Mode,
it is loaded with TC16H * 256 + TC16L and the counting
continues.
The user can modify the values in TC16H and TC16L at
any time. The new values take effect when they are load-
ed. Care must be taken not to load these registers at the
time the values are to be loaded into the counter/timer, to
ensure known operation. An initial count of 1 is not al-
lowed. An initial count of 0 will cause T16 to count from 0
to %FF FF to %FFFE. Transition from 0 to %FFFF is not a
time-out condition.
3-34
PRELIMINARY
DS97LVO0601