Read internal pin-change latches
VERSION 3.35+ of the firmware, VERSION 65+ of the DLL
Description:
This is a function to return the values of the internal pin-change latches. After reading changed latches the latches are reset.
Command Syntax: (USBm.dll)
USBm_ReadLatches( device, dataarray )
The USBm_ReadLatches function syntax has these parts:
| Part | Description |
| device | A zero-based index to address the appropriate USB device. |
| dataarray | A byte array where the returned data will be stored. Minimum size of the array must be 4 bytes |
Remarks:
Byte 0 and 2 of the modified array contain the latched value for a bit transition from 0xFF on port A (B) to any other value. If your port is pulled high with resistors (external or internal) and a button press pulls the pin low then these are the bytes to use. If your port is normally low and a button press sets a line high, then the latch data returned in bytes 1 and 3 are the appropriate bytes.
VB Declaration
| Public Declare Function USBm_ReadLatches _ Lib “USBm.dll” _ (ByVal device As Byte, _ ByRef dataarray As Byte)_ As Integer |
VB Example
| Dim dataarray(4) As Byte USBm_ReadLatches 3, dataarray(0) |
This code fragment addresses U4x1 device #3, and reads the latches into data array “dataarray“.
C Prototype
| int USBm_ReadLatches( unsigned char device, unsigned char * data ); |
C Example
| unsigned char dataarray[4]; USBm_ReadLatches( 3, *dataarray ); |
This code fragment addresses U4x1 device #3, and reads the latches into data array “dataarray“.
RobotBASIC
Raw Command Format:
| Byte Number | Description |
| 0 | 0Fh: ReadLatches |
| 1 | <not used> |
| 2 | <not used> |
| 3 | <not used> |
| 4 | <not used> |
| 5 | <not used> |
| 6 | <not used> |
| 7 | <not used> |
Raw Command Format Details:
Byte 0 contains the command. Byte 1 through byte 7 are unused.
Raw Command Response Format:
| Byte Number | Description |
| 0 | 0Fh: ReadLatches |
| 1 | Port A normally pulled high. |
| 2 | Port A normally pulled low. |
| 3 | Port B normally pulled high. |
| 4 | Port B normally pulled low. |
| 5 | <not used> |
| 6 | <not used> |
| 7 | <not used> |
Raw Command Response Format Details:
Byte 0 contains the command. Byte 1 and 3 contain the latched value for a bit transition from 0xFF on port A (B) to any other value. If your port is pulled high with resistors (external or internal) and a button press pulls the pin low then these are the bytes to use. If your port is normally low and a button press sets a line high, then the latch data returned in bytes 2 and 4 are the appropriate bytes.