Z8
®
CPU
User Manual
UM001604-0108 Clock
26
Oscillator Control
In some cases, the Z8
®
CPU offers software control of the oscillator to select low EMI
drive or standard drive. The selection is done by programming bit D7 of the Port Configu-
ration (PCON) register (see Figure 15 on page 26). The PCON register is located in
Expanded Register File Bank F, Register
00h.
A 1 in bit D7 configures the oscillator with standard drive, while a 0 configures the oscil-
lator with Low EMI drive. This only affects the drive capability of the oscillator and does
not affect the relationship of the XTAL clock frequency to the internal system clock
(SCLK).
Figure 14. External Clock Circuit
Figure 15. Port Configuration Register (Write-Only)
÷
2
OSC
External Clock
D1 (SMR)
÷
16
D0 (SMR)
D7 D6 D5 D4 D3 D2 D1 D0
PCON (Fh) 00h
Low EMI Oscillator
0 Low EMI
1 Standard
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