68HC705SP7 datasheet(102/230 Pages) FREESCALE

102 / 230 page

Parallel Input/Output

General Release Specification

MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0

Parallel Input/Output

7.6 Port Transitions

Glitches and temporary floating inputs can occur if the control bits

regarding each port I/O pin are not performed in the correct sequence.

•

Do not use read-modify-write instructions on pulldown register A

or B.

•

Avoid glitches on port pins by writing to the port data register

before changing data direction register bits from a logic zero to a

logic one.

•

Avoid a floating port input by clearing its pulldown register bit

before changing its data direction register bit from a logic one to a

logic zero.

•

The SWPDI bit in the MOR turns off all port pulldown devices and

disables software control of the pulldown devices. Reset has no

effect on the pulldown devices when the SWPDI bit is set.

•

Two or more output pins of the same port can be connected

electrically so as to provide output currents up to the sum of the

maximum specified drive currents as defined in 15.8 DC

Electrical Characteristics (5.0 Vdc) and 15.9 DC Electrical

Characteristics (3.0 Vdc). Care must be taken to assure that all

ganged pins always maintain the same output logic value.

Table 7-4. Port C Pin Functions (28-Pin Versions Only)

Port C

Pin(s)

Control Bits

PORTC Access

(Pin or Data Register)

Result on

Port C Pins

SWPDI

(in MOR)

Port C

PDICH

PDICL

DDRCx*

Read

Write

Pulldown

PC0

PC1

PC2

PC3

Data

PCx In

Data

Off

PCx In

Data

Off

PCx In

Data

Off

PCx Out

PC4

PC5

PC6

PC7

Data

PCx In

Data

Off

PCx In

Data

Off

PCx In

Data

Off

PCx Out

* DDRC can always be read or written.

X = Don’t care

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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