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32 Texas Instruments Communication Driver Manual

Bit Writes with Ladder Logic – 405 Series

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 that 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. It is necessary to write a section of Ladder Logic/Stage Programming to interpret this

value in order to change the appropriate bit. The Operator Station will write to four V memory

registers to set or reset a bit. The four registers will be consecutive starting with the Bit Write register

entered in the PLC ID field. If a Bit Write register is not entered, the register will default to V7374.

When the default register is used, V7374, V7375, V7376 and V7377 will be used to accomplish the

Bit Writes.

Register 1 This register contains a 16-bit mask in which the bit position to be set will be set to 1 and

all other bits will be set to 0.

Register 2 Each memory type has a corresponding V memory address. Register 2 contains the V

memory address in which the bit to be set is located.

Register 3 This register contains a 16-bit mask in which the bit position to be reset will be set to 0

and all other bits will be set to 1.

Register 4 This register contains the V memory address in which the bit to be reset is located.

PLC ID

The format for the PLC ID for TI 405 will include both the PLC ID and a memory register used for the

four Bit Write registers. The format will be the PLC ID followed by the memory address.

XX-VYYYYY or XX-YYYYY or XX

Where

XX PLC ID in range 1 - 90

- PLC ID/memory address separator

V Optional memory type specifier

YYYYY Optional starting with V memory address in range 1400 -7374

If a memory address is not entered, the Bit Write register will default to V7374. The following ladder

logic rungs may be added to a TI 405 program for the purpose of setting and clearing individual bits.

Siemens SIMATIC TI505 Manual de servicio Pagina 35