
Z8 Microcontrollers
ZiLOG
I/O Ports
UM001600-Z8X0599
5-29
5.9 OPEN-DRAIN CONFIGURATION
All Z8s can configure Port 2 to provide open-drain outputs
by programming the Port 3 Mode Register (P3M) bit D0=0.
Other Z8s that have a Port Configuration Register (PCON)
that can configure Port 0 and Port 1 to provide open-drain
outputs. The PCON Register is located in Expanded Reg-
ister File (ERF) Bank F, Register 00H. See Figure 5-35.
Port 1 Open-Drain (D1). Port 1 can be configured as open-
drain by resetting this bit (D1=0) or configured as push-pull
active by setting this bit (D1=1). The default value is 1.
Port 0 Open Drain (D2). Port 0 can be configured as open-
drain by resetting this bit (D2=0) or configured as push-pull
active by setting this bit (D2=1). The default value is 1.
5.10 LOW EMI EMISSION
Some Z8s can be programmed to operate in a Low EMI
Emission Mode using the Port configuration register
(PCON). The PCON register allows the oscillator and all
I/O ports to be programmed in the Low-EMI Mode inde-
pendently. Other Z8s may offer a ROM Mask or OTP pro-
gramming option to configure the Z8 Ports and oscillator
globally to a Low-EMI mode (where the XTAL frequency is
set equal to the internal system clock frequency.
Use of the Low EMI feature results in:
The output pre-drivers slew rate reduced to 10 ns
(typical).
Low EMI output drivers have resistance of 200 Ohms
(typical).
Low EMI Oscillator.
All output drivers are approximately 25 percent of the
standard drive.
Internal SCLK/TCLK = XTAL operation limited to a
maximum of 4 MHz - 250 ns cycle time, when Low EMI
Oscillator is selected and system clock (SCLK=XTAL,
SMR Reg. Bit D1=1).
Figure 5-34. Port 2 Configuration
Figure 5-35. Port Configuration Register
(PCON) (Write-Only)
D7 D6 D5 D4 D3 D2 D1 D0
(Write-Only)
0= Pull-Ups Active
1= Pull-Ups Open-Drain
Port 3 Mode Register
D7 D6 D5 D4 D3 D2 D1 D0
PCON (FH) 00H
0 Port 1 Open Drain
Port 1 Push-pull Active *
0 P34, P37 Standard Output*
1 P34, P37 Comparator Output
Comparator Output Port 3
Low EMI Oscillator
0 Low EMI
Standard *
0 Port 0 Open Drain
Port 0 Push-pull Active *
0 Port 0 Low EMI
Port 0 Standard *
0 Port 1 Low EMI
Port 1 Standard *
0 Port 2 Low EMI
Port 2 Standard *
0 Port 3 Low EMI
Port 3 Standard *
Default Setting After RESET