MC68HC908GR4MP datasheet(148/286 Pages) FREESCALE

148 / 286 page

Input/Output Ports (I/O)

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

148

Freescale Semiconductor

PTAPUE3–PTAPUE0 — Port A Input Pullup Enable Bits

These writeable bits are software programmable to enable pullup devices on an input port bit.

1 = Corresponding port A pin configured to have internal pullup

0 = Corresponding port A pin has internal pullup disconnected

16.3 Port B

Port B is a 6-bit special-function port that shares all six of its pins with the analog-to-digital converter

(ADC) module.

16.3.1 Port B Data Register

The port B data register (PTB) contains a data latch for each of the six port pins.

PTB5–PTB0 — Port B Data Bits

These read/write bits are software-programmable. Data direction of each port B pin is under the control

of the corresponding bit in data direction register B. Reset has no effect on port B data.

AD5–AD0 — Analog-to-Digital Input Bits

AD5–AD0 are pins used for the input channels to the analog-to-digital converter module. The channel

select bits in the ADC status and control register define which port B pin will be used as an ADC input

and overrides any control from the port I/O logic by forcing that pin as the input to the analog circuitry.

NOTE

Care must be taken when reading port B while applying analog voltages to

AD5–AD0 pins. If the appropriate ADC channel is not enabled, excessive

current drain may occur if analog voltages are applied to the PTBx/ADx pin,

while PTB is read as a digital input. Those ports not selected as analog

input channels are considered digital I/O ports.

PTB4 and 5 are not available in a 28-pin DIP and SOIC package

Address:

$000D

Bit 7

654321

Bit 0

Read:

0000

PTAPUE3

PTAPUE2

PTAPUE1

PTAPUE0

Write:

Reset:

00000000

= Unimplemented

Figure 16-5. Port A Input Pullup Enable Register (PTAPUE)

Address:

$0001

Bit 7

4321

Bit 0

Read:

PTB5

PTB4

PTB3

PTB2

PTB1

PTB0

Write:

Reset:

Unaffected by reset

Alternative Function:

AD5

AD4

AD3

AD2

AD1

AD0

= Unimplemented

Figure 16-6. Port B Data Register (PTB)

MC68HC908GR4MP Datasheet(PDF) 148 Page - Freescale Semiconductor, Inc

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