Twido

Summary

Main downsides:

• update speed
• setup has to be done from TwidoSoft under MS Windows.

Hardware tested

The computer was a Toshiba Satellite Pro 4310 laptop, with Debian woody and all security updates up-to-date, dual-booting to MS Windows 98.

Tested November 2002.

Main comments

Access was via the modbus_m module in RTU mode, testing with the basic_modbus demo. Outputs were observed on the status LEDs, inputs were supplied by switches (see photo); no other hardware was actually connected.

The Twido only allows acces to the internal memory registers (%M), which means that it must have a ladder program to transfer these to and from the actual inputs and outputs (at least). This program needs to be written using TwidoSoft (or from a field programmer unit).

The setup of the Twido must be done from TwidoSoft under MS Windows. To our knowledge, it is not available for Linux. We have not tested whether or not it works under wine.

Here's the setup we used in the Twido, as saved from TwidoSoft. The stepladder and the MatPLC config are also listed below.

Other notes

• The Twido only allocates the %M registers that are mentioned in the ladder program; if you try to access beyond that range, you'll get Modbus error 02 ILLEGAL DATA ADDRESS being reported by the MatPLC.
• The addresses are off-by-one: %M0 is bit number 1, %M1 is bit number 2, and so on.
• The cable needs to be in the 2 - TER DIRECT position for talking to TwidoSoft, but 3 - OTHER DIRECT for Modbus, as shown in the photo on the right.
• The port cannot be configured while TwidoSoft is Connected to the PLC. It is necessary to Disconnect (if Connected), configure the port, then Connect, transfer PC->Controller (when asked), set PLC to Run, and Disconnect. This is somewhat counter-intuitive.
• The manual says it must be in Run mode for Modbus to work; it needs to be running the ladder, anyway.
• Writing directly to the outputs (and reading directly from the inputs) is either not documented or not supported.
• Speeds above 9600 didn't work (19200, 38400).
• It seems to be a little uneven, timing-wise, more so when the inputs are also done. This may simply be a function of the communication speed.
• If MS Windows is not available, unit would have to be supplied with the ladder program already downloaded, the port configured to Modbus 9600 and the controller set to go into Run on power-up (in TwidoSoft, right-click on Software, Edit, Scan type, Configure, Automatic Run; as usual, this can only be done while Disconnected from the PLC).

Stepladder used

LD    %M0
ST    %Q0.0.0
LD    %M1
ST    %Q0.0.1
LD    %M2
ST    %Q0.0.2
LD    %M3
ST    %Q0.0.3
LD    %I0.0.0
ST    %M4
LD    %I0.0.1
ST    %M5
LD    %I0.0.2
ST    %M6
LD    %I0.0.3
ST    %M7
LD    %I0.0.4
ST    %M8
LD    %I0.0.5
ST    %M9

matplc.conf fragment

[PLC]
module modbus_m "../../io/modbus/modbus_m_rtu"

[modbus_m]
network rtu_net rtu device /dev/ttyS0 baudrate 9600 parity none data_bits 8 stop_bits 1 ignore_echo false timeout 1.5 send_retries 2

node twido rtu_net 1

map out twido.out_bit.1 L1
map out twido.out_bit.2 L2
map out twido.out_bit.3 L3
map out twido.out_bit.4 L4

map in twido.in_bit.5 sw0
map in twido.in_bit.6 sw1
map in twido.in_bit.7 sw2
map in twido.in_bit.8 sw3
map in twido.in_bit.9 sw4
map in twido.in_bit.10 sw5

$Date: 2002/11/30 11:05:00 $