Online Development Notebook > Index > Programming Overview > Device Commands > StrobeRead

StrobeRead - Read 8 bits from a port and strobe a control line


This is a function that strobes the read of a byte value from a port. This command selects port A or B for the read byte, as well as a polarity (negative or positive) and a line (A.0 - B.7) to toggle. The line is toggled to one state, the byte is read, and then the line is returned to the initial state.

Command Syntax: (USBm.dll)

USBm_StrobeRead( device, dataarray, port, sel )

The USBm_StrobeRead 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 1 byte
port The port for the byte read. A value of 00h is port A, a value of 01h is port B.
sel The strobe direction and the strobe line selection.


Bit⁄Line Selection

Byte Value Result   Byte Value Result
00h Affect A.0   08h Affect B.0
01h Affect A.1   09h Affect B.1
02h Affect A.2   0Ah Affect B.2
03h Affect A.3   0Bh Affect B.3
04h Affect A.4   0Ch Affect B.4
05h Affect A.5   0Dh Affect B.5
06h Affect A.6   0Eh Affect B.6
07h Affect A.7   0Fh Affect B.7


With sel set to the Bit⁄Line Selection values, the strobe is negative-going. By adding 10h to this value, the strobe will be positive-going. For example: 18h would pulse B.0 from low to high, and back low.

VB Declaration

Public Declare Function USBm_StrobeRead _
    Lib "USBm.dll" _
        (ByVal device As Byte, _
        ByRef dataarray As Byte, _
        ByVal port As Byte, _
        ByVal sel As Byte) _
    As Integer

VB Example

Dim dataarray(1) As Byte
    USBm_StrobeRead 1, dataarray(0), 0, &H0F

If a device is connected to the U4xx that will send a byte of data to port A when D15 is toggled from high to low and back to high, then the following commands would read this device.

First set the B.7 line high with USBm_SetBit. The line is set high to begin with because the strobe functions do not initialize the state or direction of the line. (B.7 needs to be set as an output.)

Then toggle B.7 low, read from port A, and toggle B.7 high. The breakdown of the first four bytes of the command is: 1 - device, dataarray(0) - variable to contain result, 0 - port to read (A), &H0F -  line to toggle (-F) and toggle direction (0-).

Changing to a positive strobe would necessitate changing the initial line value, and substituting &H1F for the fourth byte.

C Prototype

int USBm_StrobeRead( unsigned char device, unsigned char *data, unsigned char port, unsigned char sel );

C Example




Returns a byte value of data read from a port based on a strobing line and timing. the byte data string specifies the setup and so forth.

Raw Command

See StrobeRead2

Hardware:  U401 USB Interface    U421 USB Interface   U451 USB Interface

Programming:  USBm DLL Programming    Download Files

Application Notes:  U4x1 Application Notes    Misc Applications and Information    FAQ

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