2.3.2.2 RS-232C Serial Interface
Operating Principles
The two handshaking methods are as follows:
flag . . .
(REV) signal
The
signal is set to SPACE
when the printer can accept data and is set to MARK (–V) when
the printr is in an error state or when the empty area in the input buffer reaches 256 bytes or less.
In this way, handshaking with the host is accomplished by setting the
signal to either SPACE
or MARK. (Refer to Figure 2-46.)
( +
( -v)
[
- v )
I I
Data Bit
B i t
S t a r t
NOTES: 1.
The value of “T”
according to the input data.
2. The word structure of the serial data is:
1 start bit + 8 data bits + parity (Odd, Even, or none) + 1 or more stop bits.
Figure 2-46.
2.
X-ON/X-OFF
protocol . . . Sent over the
line
Handshaking
Handshaking is accomplished by sending either X-ON (1 1H)orX-OFF(13H) over the
line to the
host. When the printer can accept data, the printer sends an X-ON code. When the printer becomes
busy, it sends, an X-OFF code to the host computer. The X-OFF code is sent to the host when the
empty area in the printer input buffer reaches 256 bytes or less, or when the printer is in an error
state (Refer to Figure 2-47.).
+
–
-
. .
-VI
Data Bit
Bit
Start
Bit
‘T
-
J
-- --
+
‘
[
[
-- --
-- --
‘
[
[
’
-- --
–
Data
Stint
(X-OFF)
-
NOTES: 1. The value of “T”
according to the input data.
2. The word structure of the serial data is: 1 start bit + 8 data bits + parity
Even, or
none) 1 or more stop bits.
Figure 2.47.
X-ON/X-OFF
Handshaking
2 - 5 2
. . .
Содержание LQ-2550
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