Freescale Semiconductor, Inc.
Input/Output (I/O) Ports
Figure 13-7 shows the port B I/O logic.
READ DDRB ($0005)
WRITE DDRB ($0005)
DDRBx
RESET
WRITE PTB ($0001)
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
Accesses
Accesses to PTB
DDRB
Bit
PTB
Bit
I/O Pin
Mode
to DDRB
Read/Write
Read
Write
DDRB[7]
DDRB[3:0]
(1)
0
X
X
Input, Hi-Z
Output
Pin
PTB[3:0]
DDRB[7]
DDRB[3:0]
1
PTB[3:0]
PTB[3:0]
X = Don’t care
Hi-Z = High impedance
1. Writing affects data register, but does not affect input.
Advance Information
182
MC68HC908RFRK2
MOTOROLA
Input/Output (I/O) Ports
For More Information On This Product,
Go to: www.freescale.com
FREESCALE [ Freescale ]
