Owner`s manual

16
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A typical application using a Model 24H would have a host computer,
such as an IBM PC, connected to the host port, and various devices
(such as cash registers, digital laboratory instruments, bar code
readers, numerical machines, printers, modems, terminals, etc.)
connected to the peripheral ports.
Regardless of the mode of operation, the host device may connect and
send data to a specific peripheral port by sending the appropriate port
select sequence followed by the data. A port select sequence consists
of the port select code followed by the desired peripheral port number
(02 to 24) and a terminating character (0A Hex - Carriage Return or 0D
Hex - Line Feed ). The port select sequence is trapped and therefore
not passed through to the selected peripheral port.
NOTE: For demonstration purposes, we will refer to the port select
code as $SELECT. The port select code may actually be any
user-defined character string up to eight ASCII characters. The 8th bit
or parity bit is masked from the port select code before it is examined,
allowing you to send the port select code with odd or even parity.
Therefore, when 8 data bits are being sent, only the first seven data
bits are examined.
In modes of operation 2 through 5, each message sent to the host
device is preceded by a port identification number. This port
identification number consists of the port number of the peripheral port
that received the message. This number may range from 02 (for Port
2) to 24 (for Port 24).
To clear the receive buffer for a selected peripheral port, send
$SELECT followed by ASCII capital R and a terminating character (0D
Hex - Carriage Return or 0A Hex - Line Feed ). All complete or partial
messages in the buffer of the selected peripheral port will be erased
regardless of the mode of operation.