Zilog Z86193 - Manual (Page 124)

Z8
®
CPU
User Manual
UM001604-0108 Serial Input/Output
117
To configure Z8
®
CPU for a specific bit rate, appropriate values as determined by the
above equation must be loaded into registers PRE0
(
F5h
) and T0 (
F4h
). PRE0 also controls the counting mode for T0 and should therefore be
set to CONTINUOUS mode (D0 = 1).
For example, given an input clock frequency (XTAL) 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
T0 should be set to
02h
. With T0 in Continuous Mode, the value of PRE0 becomes
9Dh
(see Figure 108 ).
Table 24 lists several commonly used bit rates and the values of XTAL, p, and t required to
derive them. This list is presented for convenience and is not intended to be exhaustive.
Table 24. Bit Rates
Bit Rate
7,3728 7,9872 9,8304 11,0592 11,6736 11,9808 12,2880
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
Figure 108. Prescaler 0 Register Bit-Rate Generation
D7 D6 D5 D4 D3 D2 D1 D0
(Write-Only)
Prescalar 0 Register (PRE0)
Register F5h
Count Mode
0 = T
0
Single Pass
(Range: 1-64 decimal, 01h–00h)
(Range: 1-64)
1 = T
0
Modulo-n