315-4PN33

Modbus offers 2 different transfer modes. The mode selection hap-
pens during runtime by using the FC/SFC 216 SER_CFG.
n ASCII mode: Every byte is transferred in the 2 sign ASCII code.
The data are marked with a start and an end sign. This causes a
transparent but slow transfer.
n RTU mode: Every byte is transferred as one character. This ena-
bles a higher data pass through as the ASCII mode. Instead of
start and end sign, a time control is used.
The following Modbus Protocols are supported by the RS485 inter-
face:
n Modbus RTU Master
n Modbus ASCII Master
6.7 Modbus - Function codes
Modbus has some naming conventions:
n Modbus differentiates between bit and word access; bits = "Coils"
and words = "Register".
n Bit inputs are referred to as "Input-Status" and bit outputs as "Coil-
Status".
n word inputs are referred to as "Input-Register" and word outputs
as "Holding-Register".
Normally the access at Modbus happens by means of the ranges 0x,
1x, 3x and 4x.
0x and 1x gives you access to digital bit areas and 3x and 4x to
analog word areas.
For the CPs from VIPA is not differentiating digital and analog data,
the following assignment is valid:
0x - Bit area for master output data
Access via function code 01h, 05h, 0Fh
1x - Bit area for master input data
Access via function code 02h
3x - word area for master input data
Access via function code 04h
4x - word area for master output data
Access via function code 03h, 06h, 10h
ASCII, RTU mode
Supported Modbus pro-
tocols
Naming convention
Range definitions
VIPA System 300S Deployment PtP communication
Modbus - Function codes
HB140 | CPU | 315-4PN33 | GB | 14-43 99