3

stream into active Message Mode; i.e., the

contents of the Connection Memory Low

are output on the ST-BUS output streams

once every frame unless the ODE pin is

low. In this mode the chip behaves as if

bits 2 and 0 of every Connection Memory

High location were 1, regardless of the

actual values.

If bit 6 of the Control Register is 0, then

bits 2 and 0 of each Connection Memory

Figure 3- Address Memory Map

A5

A4

A3

A2

A1

A0

HEX ADDRESS

LOCATION

0

X

X

X

X

X

00-1F

Control Register*

1

0

0

0

0

0

20

Channel 0†

1

0

0

0

0

1

21

Channel 1†

GG

G

G

G

G

G

G

GG

G

G

G

G

G

G

GG

G

G

G

G

G

G

1

1

1

1

1

1

3F

Channel 31†

* Writing to the Control Register is the only fast transaction.

† Memory and stream are specified by the contents of the Control Register.

High location function normally (see

Figure 5). If bit 2 is 1, the associated ST-

BUS output channel is in Message Mode;

i.e., the byte in the corresponding Connec-

tion Memory Low location is transmitted

on the stream at that channel. Otherwise,

one of the bytes received on the serial

inputs is transmitted and the contents of

the Connection Memory Low define the

ST-BUS input stream and channel where

the byte is to be found (see Figure 6).

Figure 4 - Control Register Bits

76

54

32

10

Mode

Control

Bits

(Unused)

Memory

Select

Bits

Stream

Address

Bits

BIT

NAME

DESCRIPTION

7

Split

When 1, all subsequent reads are from the Data Memory

Memory

and writes are to the Connection Memory Low, except when

the Control Register is accessed again. When 0, the Memory

Select bits specify the memory for subsequent operations. In

either case, the Stream Address Bits select the subsection of

the memory which is made available.

6

Message

When 1, the contents of the Connection Memory Low are output

Mode

on the Serial Output streams except when the ODE pin is low.

When 0, the Connection Memory bits for each channel determine

what is output.

5

(unused)

4-3

Memory

0-0 - Not to be used

Select Bits

0-1 - Data Memory (read only from the microprocessor port)

1-0 - Connection Memory Low

1-1 - Connection Memory High

2-0

Stream

The number expressed in binary notation on these bits refers to

Address

the input or output ST-BUS stream which corresponds to the

Bits

subsection of memory made accessible for subsequent operations.