Datasheet

Input/Output Ports (I/O)
Technical Data MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
206 Input/Output Ports (I/O) Freescale Semiconductor
Figure 12-7. 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 12-3 summarizes
the operation of the port B pins.
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)
NOTES:
1. X = don’t care.
Input, Hi-Z
(2)
2. Hi-Z = high impedance.
DDRB[7:0] Pin
PTB[7:0]
(3)
3. Writing affects data register, but does not affect input.
1 X Output DDRB[7:0] PTB[7:0] PTB[7:0]
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
READ PTB ($0001)
PTBx
DDRBx
PTBx
INTERNAL DATA BUS