58
IM 767361-01E
Overview of the RS-232 Interface
Precautions Regarding Data Receiving Control
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
64 Bytes Free
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.
Used
192 Bytes Free
When this occurs, the
instrument waits until the free
space in the buffer reaches 192
bytes and then resumes
reception of data.
Used
Regardless of whether
handshaking is in use or not, if
the receive buffer becomes full,
the excess data will be lost.
Data Receiving Control Using Handshaking
Setting the Data Format
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.)
Data bit
(7-8 bits)
1 character
Stop bit
1
1 or 2
2
Parity bit,
EVEN, ODD,
or NONE.
Start bit
Circle idle
state
Level returns to
idle state (dotted
line) until the start
bit of the next
item of data (solid line).
1
0
