M68ICS08GR datasheet(213/408 Pages) FREESCALE

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Input/Output Ports (I/O)

Port B

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Input/Output Ports (I/O)

213

16.4 Port B

Port B is an 6-bit special-function port that shares all six of its pins with

the analog-to-digital converter (ADC) module.

16.4.1 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.

NOTE:

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

Address:

$0001

Bit 7

654321

Bit 0

Read:

PTB5

PTB4

PTB3

PTB2

PTB1

PTB0

Write:

Reset:

Unaffected by reset

Alternate

Function:

AD5

AD4

AD3

AD2

AD1

AD0

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

Freescale Semiconductor, Inc.

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