Siemens SIMATIC TI505 Instrukcja Obsługi Pobierz pdf (Strona 38)

Chapter 4: Communications Parameters 35

Bit Writes with Ladder Logic – Model 315

The Texas Instruments Hostlink Protocol does not permit an external intelligent device to directly alter

the state of a single bit without over-writing the entire byte in which the bit exists. As a result, the

Operator Station will write values to designated registers in the PLC, specifying which bit should be

set or cleared. A section of Ladder Logic/Stage Programming is necessary to interpret this value in

order to change the appropriate bit. The Operator Station will write to two consecutive bit/byte

memory registers to set or reset a bit. The starting register that the Operator Station will write to, is

determined by the register entered in the PLC ID field. If a Bit Write register is not entered, the

When the default register is used, bytes IO340 and IO350 will be used to accomplish bit writes.

The following describes the values that will be written to the memory addresses:

Byte 1 This byte will be used to set bits 0-177. To set a particular bit, the actual bit number (octal)

will be sent to this byte value. To reset the same bit, the bit number (octal) plus 200 (octal)

will be sent to this byte value.

Byte 2 This byte will be used to set bits 200-373. To set a particular bit, the actual bit number (octal)

minus 200 (octal) will be sent to this byte value. To reset the same bit, the bit number will be

sent to this byte value.

Two rungs of ladder logic will be required for each bit write. Each rung will test the individual bits

within the specified byte memory location for the bit pattern expected from the Operator Station. If

the rung is true, the logic will set or reset a particular bit as required.

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Siemens SIMATIC TI505 Instrukcja Obsługi Strona 38