68HC705JB3 datasheet(101/134 Pages) FREESCALE

101 / 134 page

November 5, 1998

GENERAL RELEASE SPECIFICATION

MC68HC05JB3

OPTICAL INTERFACE

MOTOROLA

REV 1

11-1

SECTION 11

OPTICAL INTERFACE

The MC68HC05JB3 MCU has four pairs of Optical Interfaces, conﬁgured through

Port-A. This port has built-in optical coupler interface devices, which can be

directly connected to IR displacement encoders, such as in optical mouse and

optical joystick applications.

11.1

OVERVIEW

In practical designs, each axis requires two optical couplers to detect the displace-

ment. Hence, the eight optical interfaces on port-A are enabled in pairs, with each

pair enabled by a bit in the Optical Interface Enable Register ($0E). Figure 11-1

shows a one pair of the optical interface. Table 11-1 shows the port-A conﬁgura-

tion for the four pairs.

Table 11-1. Port-A Optical Interface Pairs

For optimal performance, the reference voltage used in the optical interface

module is selectable from eight predeﬁned values, as shown in Figure 11-2. and

Table 11-2. This allows the optical interface to be easily conﬁgured by software to

match the IR displacement encoders. The reference voltage is selected using the

bits VREF0-VREF2 in the OIER.

Optical Coupler

Port pin used

Enable bit in OIER

Pair 1

PA0 and PA1

OIE0

Pair 2

PA2 and PA3

OIE1

Pair 3

PA4 and PA5

OIE2

Pair 4

PA6 and PA7

OIE3

Freescale Semiconductor, Inc.

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