105U-G Wireless Gateway
User Manual
Page 11
© September 2004
The Profibus 105G 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 105G via the fieldbus (that is, a value written to the
105G from the Profibus master). An input is a value going out from the 105G via the
fieldbus (a value read by the Profibus master).
So a Profibus Slave 105G 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 105G 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 105G 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 105G 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
bytes is 2000 (4000/8 + 750*2). The total number of I/O is 3250 which is less than the total
limit of 4300.
1.1.3
Ethernet 105G
The Ethernet 105G provides several different types of Ethernet functionality:
•
Modbus TCP. Modbus TCP uses Modbus as a base protocol within an Ethernet
communications structure. The 105G provides class 0, 1 and partially class 2 slave
functionality.
•
EtherNet IP. EtherNet IP is the version of Ethernet used by Allen-Bradley devices. The
105G provides level 2 I/O server CIP (ControlNet and DeviceNet).
•
Internet functionality. The 105G has 1.4Mbyte of non-volatile “flash” memory for
embedded web “pages” (dynamic HTTP), on-board file system, user downloadable web
pages thru FTP server, and email functionality (SMTP).
The Ethernet connection is a transformer isolated RJ45 connector, 10/100 Mbit/sec.
The Ethernet 105G I/O database has 4300 registers (each of 16 bit value), however the
Ethernet interface only supports 2048 input bytes and maximum 2048 output bytes. Each