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
ptptptptptptpt
19200 31––41––––––51
9600 32––4291––––52
4800 341314492191––54
2400 38132489419239158
1200 316134 4169 8194392 516
600 332138 432916198394 532
300 36413164649321916398 564
150 3 128 13 32 4 128 9 64 19 32 39 16 5 128
110 317531894175515742071750 8109
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
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