MC68HC08AS20 Datasheet, PDF (198/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

When bit DDRFx is a logic 1, reading address $0009 reads the PTFx
data latch. When bit DDRFx is a logic 0, reading address $0009 reads
the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 15-7 summarizes
the operation of the port F pins.
Table 15-7. Port F Pin Functions
DDRF
Bit
0
PTF
I/O Pin
Accesses
to DDRF
Accesses to PTF
Bit
Mode
Read/Write
Read
Write
X
Input, Hi-Z DDRF[3:0]
Pin
PTF[3:0]⁽¹⁾
1
X
Output
DDRF[3:0] PTF[3:0]
PTF[3:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
Advance Information
198
MC68HC08AS20 —Rev. 4.1
Freescale Semiconductor