Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 89)

3-9
IM 04L31A01-17E
Serial Interface
3
3.4 The Bit Structure of One Character and the
Operation of the Receive Buffer
The Bit Structure of One Character
The serial interface on the CX communicates using start-stop synchronization. In start-
stop synchronization, a start bit is added every time a character is transmitted. The start
bit is followed by the data bits, parity bit, and stop bit. (See the figure below.)
Data bits
(7 or 8 bits)
1 character
Start bit
Parity bit
Even, Odd, or None
Start bit
Circuit idle state
Circuit back to idle
state (dotted line)
or the start bit of the
next data (solid line)
Receive Buffer and Received Data
The data received from the PC is first placed in the receive buffer of the CX. Depending
on the available free space in the receive buffer, the received data is processed as
shown below. When the received buffer becomes full, all of the data that overflows are
discarded.
2047 bytes
Amount of used space is 1537 bytes Free
When handshaking is used, the
CX stops data reception when
data in the buffer cannot be
processed fast enough and the
amount of used space reaches
1537 bytes.
Amount of used space is
511 bytes Free
After the data reception is
stopped as described above,
data in the buffer continues to
be passed to the internal
program. When the amount of
used space falls to 511 bytes, it
resumes data reception.
Amount of used space is FULL
If the buffer becomes full in
spite of the handshaking
control, all overflow data are
discarded.