Z86D990 Datasheet, PDF (33/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
26
Open-Drain
I/O
OTP/Mask
Option
V_CC
Pull-Up
*
Pad
Out
Note: * Pull-up resistance is
about 200 KΩ at 2.3 V and
In
75 KΩ at 5.0 V with +50%
tolerance.
Figure 12. General Input/Output Pin
Read/Write Operations
The ports are accessed as general-purpose registers. Port registers are written by
specifying the port register as an instruction’s destination register. Writing to a port
causes data to be stored in the output register of the port, and reflected externally
on any bit configured as an output.
Ports are read by specifying the port register as the source register of an instruc-
tion. When an output bit is read, data on the external pin is returned. Under normal
loading conditions, returning data on the external pin is equivalent to reading the
output register. However, if a bit is defined as an open-drain output, the data
returned is the value forced on the output pin by the external system. This value
might not be the same as the data in the output register. Reading input bits also
returns data on the external pins.
PS003807-1002
PRELIMINARY