MC68HC908RK2 Datasheet, PDF (180/232 Pages) Motorola, Inc – Microcontroller Unit

Input/Output (I/O) 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 13-7 shows the port B I/O logic.
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
DDRBx
PTBx
PTBx
READ PTB ($0001)
Figure 13-7. 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 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
Accesses to PTB
Read
Write
0
X
Input, Hi-Z
DDRB[7]
DDRB[5:0]
Pin
PTB[5:0]⁽¹⁾
1
X
Output
DDRB[7]
DDRB[5:0]
PTB[5:0]
PTB[5:0]
X = Don’t care
Hi-Z = High impedance
1. Writing affects data register, but does not affect input.
Advance Information
180
Input/Output (I/O) Ports
MC68HC908RK2 — Rev. 4.0
MOTOROLA