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
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 3- Address Memory Map
A5
0
1
1
G
G
G
A4
X
0
0
G
G
G
A3
X
0
0
G
G
G
A2
X
0
0
G
G
G
A1
X
0
0
G
G
G
A0
X
0
1
G
G
G
HEX ADDRESS
LOCATION
00-1F
Control Register*
20
Channel 0†
21
Channel 1†
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.
Figure 4 - Control Register Bits
Mode
Control
Bits
(Unused)
Memory
Select
Bits
Stream
Address
Bits
7
6
5
4
3
BIT
7
NAME
Split
Memory
6
Message
Mode
DESCRIPTION
When 1, all subsequent reads are from the Data 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.
When 1, the contents of the Connection Memory Low are output
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.
0-0 - Not to be used
0-1 - Data Memory (read only from the microprocessor port)
1-0 - Connection Memory Low
1-1 - Connection Memory High
The number expressed in binary notation on these bits refers to
the input or output ST-BUS stream which corresponds to the
subsection of memory made accessible for subsequent operations.
5
4-3
(unused)
Memory
Select Bits
2-0
Stream
Address
Bits
}
2
1
0
}
}
3
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