MC68HC908AS32A Datasheet, PDF (154/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

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 13-6 shows the port B I/O logic.
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
DDRBx
PTBx
PTBx
READ PTB ($0001)
Figure 13-6. Port B I/O Circuit
When bit DDRBx is a 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a 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 13-2 summarizes the operation of the port B pins.
Table 13-2. 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
Write
Pin
PTB[7:0]⁽¹⁾
PTB[7:0]
PTB[7:0]⁽¹⁾
MC68HC908AS32A Data Sheet, Rev. 2.0
154
Freescale Semiconductor