GE CM6, Hardware Reference Manual

Page: 71 / 88

Table 33: COM1 electrical characteristics
Signal Voltage
Maximum data rate
C
L
= 1000 pF R
L
=3 K Ω
150 kbit/s
Vi (Receiver) -25 V ... +25 V
Vo (Driver) min +/- 5 V
VT+ (Receiver input threshold) max +2.7 V
VT- (Receiver input threshold ) min -2.7 V
COM2 RS422/485 Interface
The RS422/485 interface uses the Maxim® MAX1484 Transceiver chip with
following electrical characteristics:
Table 34: COM2 electrical characteristics
Signal Voltage
Maximum data rate 12 Mbit/s
Vi (driver/receiver absolute maximum) -8 V ... +12.5 V
Differential driver output (no load)
Differential driver output (R=50
Ω
RS422)
Differential driver output (R=270
Ω
RS485)
max 5 V
min 2.0 V
min 1.5 V
Driver output short current min 35 mA, max 250 mA
Receiver differential threshold min -200 mV, max 200 mV
Receiver hysteresis typ 70 mV
Receiver input resistance min 96 k Ω
Isolation
The Isolation of the Ethernet outputs is limited to 500 V peak against logic
ground (GND) and any other supply voltage.
By itself the onboard logic ground (GND) and the front panel/chassis frame
ground (FGND) are isolated on the CM6 with a layout distance of more than
0.3 mm in all PCB layers. Also standard racks (our starter cage, too) connect
both grounds at the power supply for safety reasons.
GE Intelligent Platforms – CM6 Hardware Reference Manual, Fourth Edition Page 70