ZiLOG Z8 Technical Manual

Serial I/O
The final divide-by-16 is required since TO runs
at 16 times the bit rate in order to synchronize
on the incoming data.
To configure the Z8 for a specific bit rate,
appropriate values as determined by the above
equation must be loaded into registers PREO (%F5)
and TO (%F4). PREO also controls the counting
mode for TO and should therefore be set to the
Continuous mode (Dl set to 1).
For example, given an input clock frequency
(fXTAL) of 11.9808 MHz and a selected bit rate of
1200 bits per second, the equation is satisfied by
p=39 and t=2. Counter/timer TO should be set to
%02. With TO in Continuous mode, the value of
PREO becomes %9D (Figure 12-5).
Table 12-1 lists several commonly used bit rates
and the values of fXTAL, p, and t required to
derive them. This list is presented for conven-
ience and is not intended to be exhaustive.
The bit rate generator is started by setting the
Timer Mode register TMR (%F1) bits Dl and DO both
to 1 (Figure 12-6). This transfers the contents
of the Prescaler and Counter/Timer registers to
their corresponding down-counters. In addition,
counting is enabled so that serial I/O operations
begin.
DEC
247
245
244
240
PORT 3 MODE
TO PRESCALER
TIMER/COU
NTERO
SERIAL I/O
HEX IDENTIFIERS
F7 P3M
F5
PREO
F4 TO
FO SIO
Figure 12-2. Serial I/O Register Hap
R247 P3M
Port 3 Mode Register
(% F7; Write Only)
L. pa, = INPUT
1 P30 = SERIAL IN
P37 = OUTPUT
P37 = SERIAL OUT
Figure 12-3. Port 3 Hode Register
and Bit Rate Generation
fXTAL --O--r-:-L--r:-L--r:-LS::l-- =~TE
~~~U---~CLOCK
PREO TO
Figure 12-4. Bit Rate Divide Chain
Table 12-1. Bit Rate
7,3728
7,9872
9,8304
11,0592
11,6736 11,9808 12,2880
Bit
Rate
p t
P
t
P
t
P
t
P
t
P
t
P
t
19200 3 1
--
--
4 1
--
--
--
--
--
--
5 1
9600 3
2
--
--
4 2
9 1
--
--
--
--
5
2
4800 3
4
13 1 4 4
9 2
19
1
--
--
5
4
2400
3 8 13 2
4 8
9
4
19
2
39
1
5
8
1200 3
16 13 4
4
16
9
8
19
4
39
2
5
16
600
3 32 13 8
4
32
9
16 19 8 39
4 5
32
300 3
64 13 16
4 64 9 32
19
16 39
8 5
64
150
3
128
13 32
4
128
9 64
19
32 39
16
5
128
110 3 175 3 189
4 175
5
157
4 207
17 50
8 109
12-2 3047·069,3047·025,3047·027

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English