Link characteristics
This section describes the following link characteristics of the RS-232 scanner inter-
face:
Basic operating modes
Message timing
Error detection
Basic operating modes
The RS-232 scanner interface operates in any of the following modes:
Free-flow operating mode
Software-flow operating mode
Hardware-flow operating mode
Inter-character delay operating mode
Free flow
In the free-flow operating mode, the conditions are as follows:
When the scanner receives the DTR signal, it establishes a connection with a
POS terminal, and enters the ready state.
The scanner decodes the labels immediately after power on.
The scanner optionally buffers one additional label.
The scanner sends the RTS signal, and then requests that the decoded data
from the label be sent to the POS terminal.
The scanner uses the intercharacter delay that has been configured.
Free flow with timing and flow control
In this operating mode, there is no handshake capability. The operation proceeds
as follows:
The scanner decodes a label. If you have chosen beep/lamp option 1, the
scanner beeps and the lamp comes on. (For a description of the beep/lamp
function, see page 4-16) The RTS signal is issued to notify the POS terminal
that the scanner is ready to transmit data.
The scanner begins transmitting data.
As soon as the last character of the message has been transmitted, the RTS
signal is resent. If you have chosen beep/lamp option 2, the scanner beeps
and the lamp comes on.
Another label is decoded, to begin a repetition of the cycle.
For the details of the free-flow operating mode, see Figure 4-1.
Chapter 4. RS-232 Scanner interface specifications
4-5
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