Z8 Microcontrollers
ZiLOG I/O Ports
UM001601-0803 5-17
5.5.2 Read/Write Operations
Port 3 is accessed as a General-Purpose Register P3 (03H). Port
3 is written by specifying P3 as an instruction’s destination reg
-
ister. However, Port 3 outputs cannot be written to if they are
used for special functions. When writing to Port 3, data is stored
in the output register.
Port 3 is read by specifying P3 as the source register of an in-
struction. When reading from Port 3, the data returned is both the
data on the input pins and in the output register.
5.5.3 Special Functions
Special functions for Port 3 are defined by programming the Port
3 Mode Register. By writing 0s in bit 6 through bit 1, lines
P37–P30 are configured as input/output pairs (Figure 5-22). Ta
-
ble 5-1 shows available functions for Port 3. The special func-
tions indicated in the figure are discussed in detail in their corre-
sponding sections in this manual.
Port 3 input lines P33–P30 always function as interrupt requests
regardless of the configuration specified in the Port 3 Mode Reg
-
ister.
Figure 5-21.
Port 3 Configuration with TTL Level Shifter and Auto Latch
PIN
PIN
OUT
R ≈ 500 KΩ
Auto Latch
IN
TTL Level Shifter
Port 3 Output Configuration
Port 3 Input Configuration
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