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GFK-0825F Chapter 8 Datagrams 8-3
8
Read Map
Subfunction Code: 2A hex
This datagram is used to read the reference addresses and lengths that have been configured for the
BIU’s network I/O map.
Data Field Format: none
Read Map Reply
Subfunction Code: 2B hex
A Bus Interface Unit sends this reply datagram after receiving a Read Map datagram. It contains
the previously-configured BIU network map addresses. The BIU’s network map defines the BIU
memory locations of the data that is exchanged on the bus. It provides no information about the
I/O assignments of individual I/O modules in the station. However, the checksums indicate that the
overall configuration remains unchanged.
Byte No. Byte Description
0 Not used
1 Starting reference for discrete input ( I ) data (LSB)
2 Starting reference for discrete input ( I ) data (MSB)
3 Length of discrete input ( I ) data (in bytes)
4, 5 Starting reference of analog input ( AI ) data
6 Length of analog input ( AI ) data (in bytes)
7, 8 Starting reference of discrete output ( Q ) data
9 Length of discrete output ( Q ) data (in bytes)
10,11 Starting reference of analog output ( AQ ) data
12 Length of analog output ( AQ ) data (in bytes)
13 8-bit Additive Checksum Unused
14, 15 16-bit LRC Critical Checksum (lsb in 14, msb in 15) READ ONLY
16 Field Control 8-bit Additive Checksum. Unused
17, 18 Field Control 16-bit CRC Non-Critical Checksum (lsb in 17, msb in 18) READ
ONLY
Starting references in I, AI, Q, and AQ memory are returned. For each memory type, a data length
is also supplied. If a length is zero, the associated starting reference can be ignored; it is not
meaningful.