Specifications

Bulletin No. VVDED397044US R12/00 Section 2—Modbus Plus Overview

December 2000 Command Semaphore

— Change TLP using the operator keypad or the PC software.

— Perform steps 6 and 7 to set the motor to RUN FORWARD.

12. The other nodes on the network can read all of the drive controller

registers via message handling. They cannot write to the registers

used in peer cop (in this example, they are the five registers CMD,

LFR, CMI, HSP, LSP). However, they can write to other adjustment

registers (ACC, DEC, etc.).

COMMAND SEMAPHORE

The command semaphore is a means of identifying which device the

drive controller receives its commands from. The drive controller can be

controlled locally by the logic on the terminal strip, the keypad, by the

MODBUS port the keypad plugs into, or through a fast serial link (PLC for

example). There is no configurable semaphore between the terminal

strip, the keypad, the MODBUS port, or a fast serial link.

An implicit command semaphore exists between the network nodes. If

peer cop data is enabled, none of the stations connected to the network

can write to control words. It is possible to take the command semaphore

only when peer cop data is disabled, or the drive controller is in CNF fault

mode without having lost the token. When peer cop data is disabled, the

first node to write via message handling to control words 400, 401, and

402 automatically takes the command semaphore. The drive controller

responds to this write operation by implicitly taking the command

semaphore. Only the node reserving the semaphore in this way can write

to control words. The semaphore remains reserved as long as the node

writes or reads at least once during the time-out period specified in the

8—Communication menu.

The command semaphore is released by writing bit 8 of word 400 to a

value of 1 within the specified time. Otherwise, the semaphore is freed if

no write/read operation takes place and the drive controller switches to

CNF fault mode.

NOTE: If peer cop data is again received from the network, the node

which has implicitly taken the command semaphore automatically loses

it and all requests to write to the control words via message handling are

refused by the drive controller.

The MODBUS PLUS port takes priority over the MODBUS port; if the

MODBUS PLUS port is active the drive controller’s control words cannot

be written through the MODBUS port. However, other devices can still

write to configuration words and read display words through the

MODBUS port. The MODBUS PLUS control device can release control