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Applicable Model(s)
MAP450
Title
MAP450B Network Protocol
Date
10/23/2023
Rev
01
P/N
0907-1010
Summary
Multiple MAP450 Mini-Terminals can be connected to a host controller by a multidrop network data link. To communicate on the network, the host controller and the terminals must format their messages according to the following protocol.
Solution
The MAP450 network consists of a host controller, called the network master, and a number of MAP450 Mini-Terminals connected together via the data link. All communications are initiated by the network master, which sends commands across the network data link and polls the MAP450 terminals for responses. To prevent all of the terminals on the network from responding at the same time, an addressed message scheme is used for the network protocol.
To begin communications with a particular MAP450 terminal, the network master logs on to the terminal by sending the terminal’s network address as two ASCII hexadecimal characters. This starts the communication session with that particular terminal. Once the network master has logged on to the terminal, it can communicate freely to that one terminal, sending and receiving messages until it logs off by sending a line terminator. The line terminator alerts all terminals on the network that a new communication session is about to begin, and that the next two characters sent will be a terminal’s network address.
When the network master is logged on to a single terminal, the terminal will respond to any command that requests data in the following manner. First, the terminal sends its network address as two ASCII hexadecimal digits. The requested data is sent next, followed by the current line terminator. Each command that requests data is answered separately by the terminal.
If the network master wants to send an identical message to all of the terminals on the network, it can use
the global broadcast address of “00″. By using the global address, the master can log on to all of the
terminals at once. The terminals will not transmit any data to the host when the global address is used; this
prevents the terminals from corrupting each other’s messages by trying to talk at the same time.
Sample Session
This example shows a host controller commmunicating with five MAP450 Mini-Terminals on a multidrop network. The terminals have network addresses of 01, 02, 03, 10, and 1E. The line terminator is set to an ASCII ETX character (ETX value = 03 hexadecimal). ASCII control codes are indicated by their ASCII name in SMALL CAPITALS (such as CR, LF, STX, etc.).
| Host | 00This is a global ETX | displays “This is a global” on all terminals |
| Host | 01 FF Message to #01 | log on to terminal #1, display a message |
| Host | ESC c STX | request the terminal’s configuration data |
| MAP450 #1 | 01401101 ETX | terminal #1’s data response |
| Host | ESC o STX | clear the terminal’s keyboard buffer |
| Host | ESC g1 STX ETX | sound the bell, and log off of terminal #1 |
| Host | 1E ESC ? STX ETX | log on to terminal #5, request keyboard status, log off |
| MAP450 #5 | 1E0 ETX | terminal #5’s response “0″ = no keys buffered |
| Host | 02 ESC p STX | log onto terminal #2, poll keyboard buffer |
| MAP450 #2 | 02 ETX | response, empty keyboard buffer |
| Host | FF ESC x10 STX HELLO! ETX | clear display, set cursor to column 10, display and log off |
NOTE: In the network mode, the line terminator also acts as a command terminator. This means that any
STX ETX combinations sent from the host can be shortened to just an ETX.