MC68HC908GR4MP datasheet(149/286 Pages) FREESCALE

149 / 286 page

Port B

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

Freescale Semiconductor

149

16.3.2 Data Direction Register B

Data direction register B (DDRB) determines whether each port B pin is an input or an output. Writing a 1

to a DDRB bit enables the output buffer for the corresponding port B pin; a 0 disables the output buffer.

DDRB5–DDRB0 — Data Direction Register B Bits

These read/write bits control port B data direction. Reset clears DDRB5–DDRB0], 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.

NOTE

For those devices packaged in a 28-pin DIP and SOIC package, PTB5,4

are not connected. Set DDRB5,4 to a 1 to configure PTB5,4 as outputs.

Figure 16-8 shows the port B I/O logic.

Figure 16-8. Port B I/O Circuit

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 16-3 summarizes the operation of the port B pins.

Address:

$0005

Bit 7

654321

Bit 0

Read:

DDRB5

DDRB4

DDRB3

DDRB2

DDRB1

DDRB0

Write:

Reset:

00000000

= Unimplemented

Figure 16-7. Data Direction Register B (DDRB)

READ DDRB ($0005)

WRITE DDRB ($0005)

RESET

WRITE PTB ($0001)

READ PTB ($0001)

PTBx

DDRBx

PTBx

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