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Overview of the RS-232 Interface
Precautions Regarding Data Receiving Control
Setting the Data Format
Circle idle
state
1
0
58
When handshaking is used to control the reception of data, data may still be
sent from the computer even if the free space in the receive buffer drops below
64 bytes. In this case, after the receive buffer becomes full, the excess data will
be lost whether handshaking is in effect or not. Data storage to the buffer will
begin again when there is free space in the buffer.
256 Bytes
Used
Used
Used
Data Receiving Control Using Handshaking
The RS-232 interface of this instrument performs communications using start-
stop synchronization. In start-stop synchronization, one character is transmitted
at a time. Each character consists of a start bit, data bits, a parity bit, and a stop
bit. (Refer to the figure below.)
Start bit
64 Bytes Free
192 Bytes Free
1 character
Data bit
(7-8 bits)
Parity bit,
EVEN, ODD,
or NONE.
When handshaking is in use,
the transfer of data from the
buffer to the internal program
cannot keep up with the
transmission, so the reception
of data is stopped when the
free space in the buffer reaches
64 bytes.
When this occurs, the
instrument waits until the free
space in the buffer reaches 192
bytes and then resumes
reception of data.
Regardless of whether
handshaking is in use or not, if
the receive buffer becomes full,
the excess data will be lost.
Level returns to
idle state (dotted
line) until the start
bit of the next
item of data (solid line).
Stop bit
1
1 or 2
2
IM 767361-01E
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