MC68HC908AT32 Datasheet, PDF (238/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

MC68HC08AZ32 Emulator Input/Output Ports
NOTE
Avoid glitches on port B pins by writing to the port B data register before
changing data direction register B bits from 0 to 1.
Figure 22-7 shows the port B I/O logic.
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
DDRBx
PTBx
PTBx
READ PTB ($0001)
Figure 22-7. Port B I/O Circuit
When bit DDRBx is a logic 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a
logic 0, reading address $0001 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 22-2 summarizes the operation of the port B pins.
Table 22-2. Port B Pin Functions
DDRB
Bit
PTB
Bit
I/O Pin
Mode
Accesses to
DDRB
Read/Write
0
X
Input, Hi-Z DDRB[7:0]
1
X
Output
DDRB[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
Accesses to PTB
Read
Pin
PTB[7:0]
Write
PTB[7:0]⁽¹⁾
PTB[7:0]
MC68HC908AT32 Data Sheet, Rev. 3.1
238
Freescale Semiconductor