MC68HC708MP16 Datasheet, PDF (323/398 Pages) Freescale Semiconductor, Inc – Microcontrollers

Input/Output (I/O) Ports
DDRB[7:0] — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears
DDRB[7:0], configuring all port B pins as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
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 15-7 shows the port B I/O logic.
READ DDRB ($0007)
WRITE DDRB ($0007)
RESET
WRITE PTB ($0001)
DDRBx
PTBx
PTBx
READ PTB ($0001)
Figure 15-7. 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 15-2 summarizes
the operation of the port B pins.
Table 15-2. Port B Pin Functions
DDRB
Bit
0
PTB Bit
X⁽¹⁾
I/O Pin Mode
Input, Hi-Z⁽²⁾
Accesses to
DDRB
Read/Write
DDRB[7:0]
1
X
Output
DDRB[7:0]
1. X = don’t care
2. Hi-Z = high impedance
3. Writing affects data register, but does not affect input.
Accesses to PTB
Read
Pin
Write
PTB[7:0]⁽³⁾
PTB[7:0] PTB[7:0]
MC68HC708MP16 — Rev. 3.1
Freescale Semiconductor
Input/Output (I/O) Ports
Technical Data
323