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Data Communications
MULTIPOINT CONFIGURATION
Refer to Section 3 for multipoint configuration instructions.
MULTIPOINT PROGRAMMING INFORMATION
This topic discusses programming information of interest to someone who is writing a data
communications driver or controller program to communicate with this type terminal in an
HP Multipoint environment.
HP Multipoint protocol is similar to IBM Bisynchronous communications in that it employs
control characters (embedded in the data stream) to effect an orderly transfer of data between
the host computer program and the various terminals.
Multipoint operation requires the following:
• All communications follow a strict protocol.
• Each terminal must have an address that is unique within its communication line.
• Data is transmitted in blocks.
• All data transfers are initiated by the computer.
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• All terminals on the same communication line must use the same transmission format
(asynchronous or synchronous), the same type of transmission code (ASCII7/ASCIIB), the
same type of parity (O's, ODD, or EVEN), and the same baud rate.
Polling and Selecting
All data transfers are initiated by the computer in one of two ways, polling or selecting. In both
cases, device addresses are used to identify the desired terminal or group of terminals.
TERMINAL ADDRESSES. Each terminal in an HP Multipoint configuration must have an
address that is unique on the communications line on which it is connected (the same address
can, however, be used on two different lines). An address is made up ofa one-character group ID
(GID) and a one-character device ID (DID) (figure 7-10).
7-23
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