4.13 - Asynch [U12 Datasheet] | LabJack
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4.13 - Asynch [U12 Datasheet]

Requires firmware V1.1 or higher. This function writes and then reads half-duplex asynchronous data on 1 of two pairs of D lines (8,n,1). Call AsynchConfig to set the baud rate. Similar to RS232, except that logic is normal CMOS/TTL (0=low=GND, 1=high=+5V, idle state of transmit line is high). Connection to a normal RS232 device will probably require a converter chip such as the MAX233.

Execution time for this function is about 20 milliseconds to write and/or read up to 4 bytes, plus about 20 milliseconds for each additional 4 bytes written or read. Slow baud rates can result in longer execution time.

PortA => TX is D8 and RX is D9
PortB => TX is D10 and RX is D11
Transmit Enable is D12

Up to 18 bytes can be written and read. If more than 4 bytes are written or read, this function uses calls to WriteMem/ReadMem to load/read the LabJack’s data buffer.


long Asynch (    long *idnum,
                 long demo,
                 long portB,
                 long enableTE,
                 long enableTO,
                 long enableDel,
                 long baudrate,
                 long numWrite,
                 long numRead,
                 long *data )

Parameter Description:
Returns: LabJack errorcodes or 0 for no error.

  • *idnum – Local ID, serial number, or -1 for first found.
  • demo – Send 0 for normal operation, >0 for demo mode. Demo mode allows this function to be called without a LabJack.
  • portB – If >0, asynch PortB is used instead of PortA.
  • enableTE – If >0, D12 (Transmit Enable) is set high during transmit and low during receive.
  • enableTO – If >0, timeout is enabled for the receive phase (per byte).
  • enableDel – If >0, a 1 bit delay is inserted between each transmit byte.
  • baudrate – This is the bps as set by AsynchConfig. Asynch needs this so it has an idea how long the transfer should take.
  • numWrite – Number of bytes to write (0-18).
  • numRead – Number of bytes to read (0-18).
  • *data – Serial data buffer. Send an 18 element array. Fill unused locations with zeros.


  • *idnum – Returns the local ID or –1 if no LabJack is found.
  • *data – Serial data buffer. Returns any serial read data. Unused locations are filled with 9999s.

ActiveX Function Differences:
The maximum number of bytes to read and/or write is limited to 6 (numWrite and numRead should be 0-6). The data array is replaced with pointers to 6 individual data bytes.

Declaration (ActiveX):

long AsynchX (    long FAR* idnum,
                  long demo,
                  long portB,
                  long enableTE,
                  long enableTO,
                  long enableDel,
                  long baudrate,
                  long numWrite,
                  long numRead,
                  long FAR* data0,
                  long FAR* data1,
                  long FAR* data2,
                  long FAR* data3,
                  long FAR* data4,
                  long FAR* data5 )