Chapter 4. Ladder Diagram (LD) ProgrammingGFK-2950C February 2018 1514.8.6 Communication Request (COMMREQ)The Communication Request (COMMREQ) function communicates with anintelligent module, such as a Genius Communications Module or High SpeedCounter.Notes:▪ The information presented in this section shows only the basic format of the COMMREQfunction. Many types of COMMREQs have been defined. You will need additional information toprogram the COMMREQ for each type of device. Programming requirements for each modulethat uses the COMMREQ function are described in the specialty module's user documentation.▪ If you are using the COMMREQ to conduct serial communications, refer to the Serial I/O, SNP andRTU Protocols section in PACSystems RX7i, RX3i and RSTi-EP CPU Reference Manual, GFK-2222.▪ If you are using the COMMREQ to interface with an intelligent module (such as GeniusCommunications Gateway), refer to that product’s user manual for operational details.▪ A COMMREQ instruction inside an interrupt block being executed may cause the block to bepreempted when a new, incoming interrupt has the same priority.When COMMREQ receives power flow, it sends the command block of data specified by the INoperand to the communications TASK in the intelligent or specialty module, at the rack/slot locationspecified by the SYSID operand. The command block contents are sent to the receiving device andthe program execution resumes immediately. (Because PACSystems does not support WAIT modeCOMMREQs, the timeout value is ignored.)The COMMREQ passes power flow unless the following fault conditions exist. The Function Faulted(FT) output may be set ON if:▪ Control block is invalid▪ Destination is invalid (target module is not present or is faulted)▪ Target module cannot receive mail because its queue is fullThe Function Faulted output may have these states:Enable Error? Function Faulted Outputactive no OFFactive yes ONnot active no execution OFFCommand BlockThe command block provides information to the intelligent module on the command to beperformed. The command block starts at the reference specified by the operand IN. This addressmay be in any word-oriented area of memory (%R, %P, %L, %W, %AI, %AQ, or symbolic non-discretevariables). The length of the command block depends on the amount of data sent to the device.The Command Block contains the data to be communicated to the other device, plus informationrelated to the execution of the COMMREQ. Information required for the command block can beplaced in the designated memory area using a programming function such as MOVE, BLKMOV, orDATA_INIT_COMM.
