WI-GTWY-9-xxx Wireless Gateway
User Manual V1.18
11
The Modbus/DF1 WI-GTWY-9-MD1 has 4300 general-purpose I/O registers. Each discrete,
analog and pulse I/O point takes up one register.
1.1.2
Profibus WI-GTWY-9-PRx
The Profibus WI-GTWY-9-PR1 provides Profibus-DP Slave functionality according to EN
50170. Profibus is a popular automation fieldbus that originated in Germany and is used
extensively by Siemens and other automation suppliers.
The Profibus connection on the WI-GTWY-9-PRx is optically isolated RS485 using an on-board
DC/DC converter. The Profibus port has automatic baudrate detection (9600 bit/s - 12 Mbit/s).
The Profibus Slave WI-GTWY-9-PR1 will connect to a Profibus LAN controlled by an external
master device. The Profibus Master WI-GTWY-9-PR2 will control communications on a
Profibus LAN, and can connect to up to 125 Profibus slave devices.
The Profibus WI-GTWY-9-PR2 I/O database has 4300 registers (each of 16 bit value), however
the Profibus interface limits the amount of I/O that can be transferred via the Profibus port.
Slave unit (PR1). The PR1 slave unit only supports 416 x 8 bit bytes of I/O. Of the 416 bytes of
I/O, there is a maximum 244 input bytes and maximum 244 output bytes - that is, if 244 input
bytes are used then only 172 output bytes can be used (416 – 244). Each byte can represent 8
discrete inputs or outputs, or an 8-bit value, or two bytes can represent a 16-bit value. That is,
analog or pulse I/O can be transferred as 8-bit registers (1 byte) or 16-bit registers (2 consecutive
bytes).
An “output” is a value coming into the WI-GTWY-9-PR1 via the fieldbus (that is, a value
written to the WI-GTWY-9-PR1 from the Profibus master). An input is a value going out from
the WI-GTWY-9-PR2 via the fieldbus (a value read by the Profibus master).
So a Profibus Slave WI-GTWY-9-PR1 could handle up to 1952 (244 x 8) discrete inputs or 244
low resolution analog inputs or 122 (244 x ½) high resolution analog inputs, or some
combination in between.
For example, a Profibus WI-GTWY-9-PR1 can handle 400 discrete inputs, 240 discrete outputs,
90 analog inputs and 60 analog outputs (assume analogs are 16-bit). The number of input bytes
is 230 (400/8 + 90*2). The number of output bytes is 150 (240/8 + 60*2). The total number of
I/O bytes is 380. If the number of analog outputs was increased to 90, then the total output bytes
would be 210 (240/8 + 90*2), and the total number of I/O bytes is 440 - this exceeds the
capacity of the Profibus interface.
Master unit (PR2). The Profibus master interface supports 2048 input bytes and 2048 output
bytes. Each byte can be 8 discrete inputs or outputs, but analog or pulse I/O take up 1 byte for
low resolution values (8-bit) or 2 bytes for high resolution values (16-bit).
So a Profibus Master WI-GTWY-9-PR2 can handle up to 4300 I/O total, but analog or pulse
inputs are limited to 2048 x 8-bit values or 1024 x 16-bit values. The same limit applies to
outputs.
For example, a Profibus Master WI-GTWY-9-PR2 can handle 2000 discrete inputs and 500
analog inputs (assume analogs are 16-bit). The number of input bytes is 1250 (2000/8 + 500*2).
The same unit could handle 4000 discrete outputs and 750 analog outputs. The number of output
