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Pin
Signal
Pin 6
V+
Pin 7
V+
Pin 8
GND
Pin 9
GND
RS485 Addresses
The addresses are outlined in Table 5.
Table 5: RS485 Addresses
Address
0
2 to 31
255
Each SKB switch is pre-assigned an address of 1. If an SKB device is reset (either hard or soft),
and the network address is 1, the ATTN line is asserted. The ATTN line is de-asserted when the
device address is changed to something other than 1. This feature acts as a mechanism for
informing the bus master that a device with the default address is connected to the bus.
RS485 Protocol
A proprietary link-layer RS485 protocol has been developed that enables network-based
communication utilizing a single master and multiple slaves on a common bus. The protocol
provides a high-level flow control mechanism (using acknowledge packets) and link-layer error
detection (using CRC packet validation). The RS485 protocol consists of two elements: the RS-
485 link-layer communication packet and the master-slave acknowledge cycle.
The RS485 packet is composed of a number of bytes surrounding a data payload (Figure 9). The
data payload section of the RS485 packet holds exactly one standard command packet, as
illustrated. The packet bytes are designated as shown in Table 6.
Description
5 V supplies in
5 V supplies in
power ground
power ground
Reserved for master. Cannot be an SKB switch.
Valid address range for SKB devices.
Broadcast address. Packets sent with a broadcast address are received
and parsed by all active SKB devices on the RS485 bus.
Functionality
These lines are supplied by a 5V ±5%
regulated power supply provided from
the host. Each of these wires provides
power for different elements of the
module.
These lines are power supply grounds
and are isolated from the chassis
ground.
Description
Operating and Maintenance Instructions – 17
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