National Instruments GPIB-232CV, Руководство пользователя

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Operation Chapter 3
GPIB-232CV User Manual 3-8 © National Instruments Corp.
Buffering and Handshaking
Two protection mechanisms are used to ensure that the GPIB-232CV does
not lose incoming serial data: data buffering and handshaking.
The GPIB-232CV has an internal RAM buffer that stores incoming serial
data until it can output the data to the GPIB port. The size of this RAM
buffer, in part, determines how much serial data the GPIB-232CV can
accept until its buffer overflows. The GPIB-232CV comes equipped with a
256 KB RAM buffer.
When its RAM buffer is nearly full, the GPIB-232CV can handshake with the
serial host to stop data transmission. When the buffer is almost empty, the
GPIB-232CV can again handshake with the serial host to start data
transmission. The GPIB-232CV is capable of using both the XON/XOFF and
the hardware handshaking protocols. The hardware handshake is always
active during RS-232 transfers. The XON/XOFF protocol is enabled or
disabled by properly setting the internal configuration switch.
Hardware Handshake
The hardware handshake function is always active during RS-232 transfers
and uses the RTS and CTS signal lines. When the GPIB-232CV is ready to
accept serial data, it asserts the RTS line. This signal remains asserted until
the GPIB-232CV's data buffer is almost full. At this point, the
GPIB-232CV unasserts the RTS line, signaling to the serial host that the
GPIB-232CV is no longer ready to accept data. The serial host should
monitor the RTS line and suspend data transmission whenever the RTS line
becomes unasserted.
The GPIB-232CV is also able to suspend transmission when the serial host
is no longer ready to accept data. The GPIB-232CV is configured to
immediately stop transmission of serial data when CTS becomes
unasserted.
Note: If you use a serial cable that does not connect to CTS, CTS will
not be asserted and the GPIB-232CV will not transmit data.