Epson LQ-2550 Technical Manual page 99

2.3.2.2 RS-232C Serial Interface
Operating Principles
The two handshaking methods are as follows:
The DTR signal is set to SPACE (+V) 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 DTR signal to either SPACE
or MARK. (Refer to Figure 2-46.)
( + v)
( -v)
[ +V)
NOTES: 1.
The value of "T" veries 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.
2. protocol . . . Sent over the TXD line
X-ON/X-OFF
Handshaking is accomplished by sending either X-ON (1 1H)orX-OFF(13H) over the TXD 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.).
–
NOTES: 1. The value of "T" veries 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.
S t a r t
Figure 2-46. DTR
Data Bit
Start
Bit
Figure 2.47.
X-ON/X-OFF
Data Bit
Handshaking
-
-- --
' [ [
-- --
Data Blt
Handshaking
2 - 5 2
I I
B i t "'
-
'T
J
-- --
[ [ '
-- --
Stint D~tao~;t
-
. . . . .