Datasheet

Table Of Contents
Port B
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
Freescale Semiconductor 139
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 12-8 shows the port B I/O logic.
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 12-3 summarizes the operation of the port B pins.
Figure 12-8. Port B I/O Circuit
Table 12-3. Port B Pin Functions
DDRB
Bit
PTB
Bit
I/O Pin
Mode
Accesses to DDRB Accesses to PTB
Read/Write Read Write
0
X
(1)
1. X = Don’t care
Input, Hi-Z
(2)
2. Hi-Z = High impedance
DDRB7–DDRB0 Pin
PTB7–PTB0
(3)
3. Writing affects data register, but does not affect input.
1 X Output DDRB7–DDRB0 PTB7–PTB0 PTB7–PTB0
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
READ PTB ($0001)
PTBx
DDRBx
PTBx
INTERNAL DATA BUS