MC68HC705MC4 Datasheet, PDF(42/99 Page) Motorola, Inc

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MC68HC705MC4 Datasheet, PDF (42/99 Pages) Motorola, Inc – Microcontrollers　

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MC68HC705MC4 Specification Rev. 1.5

SECTION 6

INPUT/OUTPUT PORTS

In the User Mode, there are 20 bidirectional I/O lines arranged as two 8-bit I/O ports (Ports

A and C), one 4-bit I/O port (Port B), and one 2-bit Input port (Port D). These ports are

programmable as either inputs or outputs, except Port D7, under software control of the

data direction registers (DDRs).

6.1 PORT A

Port A is an 8-bit bidirectional port that shares PA1-PA6 with the PWM subsystem. (See

Figure 6-1: Port A I/O Circuitry.) The Port A data register is located at address $0000

and its Data Direction Register (DDR) is located at address $0004. Reset does not affect

the data registers, but clears the DDRs, thereby setting all of the port pins to input mode.

Writing a one to a DDR bit sets the corresponding port pin to output mode. PA1-PA6 may

be used for general I/O applications when the PWM subsystem is disabled. PA0-7 feature

larger P-channel output devices and are capable of sourcing more current than a standard

port (refer to SECTION 12: ELECTRICAL SPECIFICATIONS).

Read $0004

Write $0004

Write $0000

Reset

(RST)

Data Direction

Data

I/O

Output

Read $0000

Internal HC05

Data Bus

Figure 6-1: Port A I/O Circuitry

6.1.1 MCU LINE INTERFACE RECOMMENDATIONS

It is expected that some applications appropriate to the MC68HC705MC4 will be required

to determine the presence of line (mains) voltage using the MCU. A low-cost MCU line

interface is shown in Figure 6-2: Line Interface Circuitry. PA7 has been intentionally

located between VDD and VSS to provide a lowest possible impedance path for the injected

currents in particular fast transients. Although any I/O port will function in this manner, it

is recommended that only PA7 be used for such an interface. The positive and negative

excursions of the input voltage relative to the neutral return are clamped between VSS and

VDD using the internal parasitic input diodes. The series resistor limits the injected currents

to the specified value. (Refer to SECTION 12 ELECTRICAL SPECIFICATIONS.) The

resistor value must be calculated based upon maximum expected transient voltage levels

Section 6: Input/Output Ports

MOTOROLA

Page 33

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