7.The Command String

The following chapter explains the structure of both types of dedicated protocol format for the α2 Series Controller. The 8-bit binary protocol is available in two different formats:

1 ) Format A

2 ) Format B

The Dedicated Protocol is based on a PC or Peripheral device sending messages to the α2 controller and in return receiving replies to those commands. The string of data that accomplishes these tasks is called the Command String. The Command String can be used to check the communication line, read/write from/to internal bit/word data, perform remote Run/ Stop operation with the controller, and to edit Time Switch data. The data contained in the Command String varies with the type of action to be accomplished.

Two formats have been designed to carry the data - Format “A” for simple Communication line checks and Format “B” for the more involved data processing instructions. The information to construct and read Command Strings is explained in this chapter.

Communication between the computer and the α2 Series Controller is handled using interrupts. The Transmit/Receive process is completed after the last operation has been completed in the Function block sequence order. Refer to the Communication Timing section for further information concerning response delay time.

Notes:

Communication requirements

a ) Power to the α2 Series Controller

b ) Switching the Serial Com mode to Dedicated Protocol. Using the front panel keys select “Serial Com” from the “others...” menu. Select “Other Com” then proceed to cycle the power to accept the setting. Or, using AL-VLS/WIN-E please refer to Chapter 6.

Communication Settings

“Serial Com” from the “others...” menu. Select “Other Com” and adjust the “ComFormat, Station No. and Link Block” accordingly. Refer to Chapter 6 for detailed information concerning Front panel screen. However, the user can also set the default communication dedicated protocol settings from the VLS software.

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