Zilog Z8PE002 - Manual (Page 33)

Z8PE002
ZiLOG Z8Plus OTP Microcontroller
DS008700-Z8X0799 P R E L I M I N A R Y 33
RESET CONDITIONS
After a RESET , the timers are disabled. See Table 8 for timer
control, value, and auto-initialization register status after
RESET .
I/O PORTS
The Z8Plus dedicates 14 lines to input and output. These lines
are grouped into two ports known as Port A and Port B. Port
A is an 8-bit port, bit programmable as either inputs or outputs.
Port B can be programmed to provide either standard in-
put/output, or the following special functions:
T0 output,
comparator input, SMR input, and external interrupt inputs.
All pins except PB5 include push-pull CMOS outputs. In
addition, the outputs of Port A on a bit-wise basis can be
configured for open-drain operation.The ports operate on
a bit-wise basis. As such, the register values for/at a given
bit position only affect the bit in question.
Each port is defined by a set of four control registers (Figure 26).
Directional Control and Special Function
Registers
Each port on the Z8Plus features a dedicated directional con-
trol register that determines (on a bit-wise basis) if a given
port bit operates as input or output.
Each port on the Z8Plus features a special function register
(
SFR ) that, in conjunction with the directional control reg-
ister, implements (on a bit-by-bit basis) any special func-
tionality that can be defined for each particular port bit.
Input and Output Value Registers
Each port features an Output Value Register and an input
value register. For port bits configured as an input by means
of the directional control register, the input value register
Figure 26. Port A Configuration with Open-Drain Capability and Schmitt-Trigger
PIN
PA0–PA7
PTAIN Bit n
N = 0...7
PTAOUT Bit n
N = 0...7
PTASFR Bit n
N = 0...7
PTADIR Bit n
N = 0...7
Table 14. I/O Ports Registers
Register Address Identifier
Port B Special Function 0D7H PTBSFR
Port B Directional Control 0D6H PTBDIR
Port B Output Value 0D5H PTBOUT
Port B Input Value 0D4H PTBIN
Port A Special Function 0D3H PTASFR
Port A Directional Control 0D2H PTADIR
Port A Output Value 0D1H PTAOUT
Port A Input Value 0D0H PTAIN