MB_DIRd() is called when a Modbus master sends a Function Code 2 command. MB_DIRd() read the value of a single discrete input. MB_DIRd() should only be called by µC/Modbus.
Prototype
CPU_BOOLEAN MB_DIRd (CPU_INT16U di,
CPU_INT16U * perr)
Arguments
di
Is the discrete input number that you want to read and can be a number between 0 and 65535 (depending on your product). It is up to you to decide which discrete input is assigned to what variable in your product.
perr
Is a pointer to a variable that will contain an error code based on the outcome of the call. Your code thus needs to return one of the following error codes:
MODBUS_ERR_NONE
if the discrete input number you specified is a valid discrete input and you are able to have code access the value of this discrete input.
MODBUS_ERR_RANGE
if the discrete input number passed as an argument is not a valid discrete input number for your product.
Returned Value
MB_DIRd() returns the current value of the specified discrete input (TRUE or FALSE). If an invalid discrete input number is specified, you should return FALSE.
Notes / Warnings
Code is enabled when MODBUS_CFG_FC02_EN is set to DEF_ENABLED in your product’s mb_cfg.h file.
Called By:
MBS_FC02_DIRd() in mbs_core.c
Example
In this example, our product has 19 discrete inputs. 16 of these discrete are placed in AppDITbl[] by your application. The other three discrete inputs actually represent the status of three switches that your application reads and places the status into the following variables: AppSwStart, AppSwStop and AppSwReset. A pressed switch is indicated by a TRUE and a released switch is represented by a FALSE.
Your systems Engineer decided to assign Modbus discrete input numbers 100, 101 and 102 to the three switches and the other discrete inputs to 103 through 118.