68HC705JB4 datasheet(47/134 Pages) FREESCALE

47 / 134 page

February 24, 1999

GENERAL RELEASE SPECIFICATION

MC68HC05JB4

INPUT/OUTPUT PORTS

MOTOROLA

REV 2

7-1

SECTION 7

INPUT/OUTPUT PORTS

In normal operating mode there are 19 usable bidirectional I/O lines arranged as

one 8-bit I/O port (Port-A), one 5-bit I/O port (Port-B), and one 6-bit I/O port

(Port C). The individual bits in these ports are programmable as either inputs or

outputs under software control by the data direction registers (DDRs).

Each pin on Port-A and Port-B has individual internal pull-up resistor (50k

Ω typi-

cal) which can be enabled by software. In addition, port pins PA6, PA7, and all

port-B pins have built in Slow Falling Edge transition feature. This software select-

able feature helps to eliminate EMI noise.

Other functions such as high current drive, interrupt, are available on some port

pins via mask option.

7.1

SLOW FALLING-EDGE OUTPUT DRIVER

When enabled, the slow falling-edge output drive feature has a slow falling edge

(drops from 5.0V to 2.2V in 167ns typically, with 50pF load) followed by a fast tran-

sition to Vss. The fast transition duration is depending on the strength of the output

driver deﬁned for each port.

Figure 7-1. Slow Falling-edge Output Driver

50pF

5.0V

165ns

330ns

2.2V

Output Driver

Freescale Semiconductor, Inc.

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68HC705JB4 Datasheet(PDF) 47 Page - Freescale Semiconductor, Inc