Applicable Model(s)



MAP450B Network Protocol








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.


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.).

Host00This is a global ETXdisplays “This is a global” on all terminals
Host01 FF Message to #01log on to terminal #1, display a message
HostESC c STXrequest the terminal’s configuration data
MAP450 #101401101 ETXterminal #1’s data response
HostESC o STXclear the terminal’s keyboard buffer
HostESC g1 STX ETXsound the bell, and log off of terminal #1
Host1E ESC ? STX ETXlog on to terminal #5, request keyboard status, log off
MAP450 #51E0 ETXterminal #5’s response “0″ = no keys buffered
Host02 ESC p STXlog onto terminal #2, poll keyboard buffer
MAP450 #202 ETXresponse, empty keyboard buffer
HostFF ESC x10 STX HELLO! ETXclear 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.

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