Ma Current Loop - Intermec EasyCoder 501 Service Manual

18.4 20 mA Current
Loop
Intermec EasyCoder 501 – Service Manual Ed. 7
The 20 mA current loop interface is a single-ended, full duplex
serial interface which uses current instead of voltage to transmit
signals on a four-wire line. 20 mA current corresponds to a logical
"0" and 0 mA corresponds to a logical "1".
Optocouplers are used to separate the transmission line from the
internal logics of the printer and the host computer. Therefore this
interface is suitable where electrical interference may occur, and
for transmission over longer distances (up to 500 metres or 1,500
ft.).
Depending on the confi guration of the connection cable between
printer and host computer, the printer can work either active (that
is, supplying the current) or passive. A transmission speed between
300 and 9,600 baud is recommended.
- +
P203
IC-205
IC-206
Chapter 18 "uart1:"
P-203
(external +5V)
P-202
(interface select)
P202
232
CL
422
IC-205 & IC-206
(optocouplers)
153