This function is called from YOUR application code to read coils from a Modbus slave.
Prototype
CPU_INT16U MBM_FC01_CoilRd (MODBUS_CH *pch,
CPU_INT08U slave_addr,
CPU_INT16U start_addr,
CPU_INT08U *p_coil_tbl,
CPU_INT16U nbr_coils);Arguments
pch
is a pointer to the channel (returned by MB_CfgCh()). This pointer specifies onto which channel the Modbus master will be communicating on. Of course, ‘pch’ must have been configured as a Master when you configured the channel.
slave_addr
specifies the slave ‘node address’ that you desire to read the coil information from. This can be a number between 1 and 255 but needs to match the number assigned to the slave node.
start_addr
specifies the start addres of the coil number. This can be from 0 to 65535.
pcoil_tbl
is a pointer to an array of 8 bit values that will receive the value of all the coils you are reading. The size of the array needs to be at least (nbr_coils - 1) / 8 + 1. The format of the table is as follows:
MSB LSB
B7 B6 B5 B4 B3 B2 B1 B0
-------------------------------------
p_coil_tbl[0] #8 #7 #1
p_coil_tbl[1] #16 #15 #9
:
:nbr_coils
specifies the number of coils you want to read from the slave.
Returned Value
MODBUS_ERR_NONE
if the call was successful.
MODBUS_ERR_RX
if a response was not received from the slave within the timeout specified for this channel (see MB_CfgCh()).
MODBUS_ERR_SLAVE_ADDR
If the transmitted slave address doesn't correspond to the received slave address
MODBUS_ERR_FC
If the transmitted function code doesn't correspond to the received function code
MODBUS_ERR_BYTE_COUNT
If the expected number of bytes to receive doesn't correspond to the number of bytes received.
Notes / Warnings
None
Called By
Your Modbus master application.