> For the complete documentation index, see [llms.txt](https://support.powerio.com/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.powerio.com/hub/codesys-hvac/en/hvac-modbus-library/functionblocks/generic/simplereadcoilinput.md).
# SimpleReadCoilInput
## `SimpleReadCoilInput` (FB)
`FUNCTION_BLOCK` SimpleReadCoilInput
### Representation
### Evaluation of the actual values for function codes 01 (Read Coils) or 02 (Read Discrete Inputs)
When evaluating the actual values, only the output `arxValue` must be considered. This is an array with 64 elements of type `BOOL` (1 - 64 Coils / Inputs).
The specification of the bits to be transmitted is primarily determined by the choice of the function code (eFunctionCode), the start address (wStartAddr) and the desired number of Coils / Inputs (`wNumberOfCoils`) in the range 1 - 64.
The actual values are available as follows:
The first element `arxValue[0]` contains the state of the coil with the number `wStartAddress` The second element `arxValue[1]` contains the state of the coil with the number `wStartAddress` + 1 The third element `arxValue[2]` contains the state of the coil with the number `wStartAddress` + 2, etc. Unused elements of `arxValue` are described with FALSE.
Task: Read the actual value of coil 17
Settings: eFunctionCode: ReadFunctionCodesCoilInput.FC01\_ReadCoils wStartAddr = 17 wNumberOfCoils = 1
`arxValue[0]`: Actual value of coil 17 `arxValue[1]`: FALSE `arxValue[2]`: FALSE … `arxValue[63]`: FALSE
### CODESYS
InOut:
| Scope | Name | Type | Initial | Comment |
| ----------- | ------------------- | -------------------------------------- | -------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- |
| Input | `xEn` | `BOOL` | TRUE | Enable / disable communication (TRUE = enable) |
| Input | `byUnitId` | `BYTE` | 0 | Device address |
| Input | `xUpdateActual` | `BOOL` | FALSE | Update of actual values (on every rising edge) |
| Input | `xResError` | `BOOL` | FALSE |
Reinitialization of the outputs eErrorCodeCom or eErrorCodeDev to the error-free state (on every rising edge)
|
| Inout | `ModbusClient` | `ModbusClientBase` | | Client of the device |
| Output | `eFunctionCodeFb` | ReadFunctionCodesCoilsInputs | | Feedback - Modbus function code for the Modbus telegram |
| Output | `wStartAddrFb` | `WORD` | | Feedback - Start address of the coils/inputs to be read |
| Output | `wNumberOfCoilsFb` | `WORD` | | Feedback - Number of coils/inputs to be read (1 - 64) |
| Output | `arxValue` | `ARRAY` \[0 .. 63] `OF` `BOOL` | | Array with the current coil/input states |
| Output | `xAlarm` | `BOOL` | | Collective fault (TRUE = fault) |
| Output | `xAlarmCom` | `BOOL` | | Collective fault - communication (TRUE = fault) |
| Output | `eErrorCodeCom` | ModbusErrorCode | | Error code - communication (0 = no error) |
| Output | `eErrorCodeDev` | SIMPLE\_READ\_COIL\_INPUT\_ERROR\_CODE | | Error code - device (0 = no error) |
| Output | `xBusy` | `BOOL` | | Communication indicator (TRUE = communication) |
| Input Const | `wNumberOfCoils` | `WORD` | 1 | Number of coils/inputs to be read (1 - 64) |
| Input Const | `eFunctionCode` | ReadFunctionCodesCoilsInputs | ReadFunctionCodesCoilsInputs.FC01\_ReadCoils | Modbus function code for the Modbus telegram |
| Input Const | `wStartAddr` | `WORD` | | Start address of the coils/inputs to be read |
| Input Const | `tTimeUpdateActual` | `TIME` | TIME#3s0ms |
Update interval for the processes influenced by the input xUpdateActual influenced
|
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