How Do I Reverse the ACK and REQ Pin Assignments for NI 653x Devices in LabWindows/CVI?
Primary Software: LabWindows/CVI Development Systems>>Full Development System
Primary Software Version: 7.1
Primary Software Fixed Version: N/A
Secondary Software: LabWindows/CVI Development Systems>>Base Package
Problem: The NI 653X User Manual states that in order to perform handshaking I/O between two NI 653X devices using an SH-68-68-D1 cable, you need to reverse the ACK and REQ pin assignments. How is this done in LabWindows/CVI using Traditional NI-DAQ?
Solution: To perform this task in LabWindows/CVI, you need to set the
ACK-REQ Exchange attribute to ON using a Traditional NI-DAQ function called
Set_DAQ_Device_Info. To locate the
Set_DAQ_Device_Info function in LabWindows/CVI, follow the steps below:
- Launch LabWindows/CVI.
- Verify the Library Tree is visible by browsing to View»Library Tree and making sure there is a checkmark next to Library Tree.
- Expand the Library Tree to the path Libraries » Traditional NI-DAQ Library » Initialization/Utilities » Set_DAQ_Device_Info.
Right-clicking the function name and selecting
Show Function Panel brings up the dialog box shown below.
A majority of the attributes for the Set_DAQ_Device_Info function can be selected using the Type of Information and Information Value drop-down menus. However, the attribute ACK-REQ Exchange, is not an available drop-down menu feature. Therefore in order to use this attribute, manual text entry is required. The correct syntax for this function can be found in the Traditional NI-DAQ (Legacy) C Function Reference Help file located at Start » All Programs » National Instruments » NI-DAQ. Shown below is the correct syntax for this function.
status = Set_DAQ_Device_Info (deviceNumber, infoType, infoValue)
The first parameter,
deviceNumber, is assigned by Measurement and Automation Explorer to represent your data acquisition card. The second parameter,
infoType , represents the attribute that needs to be changed. The two options for exchanging the ACK and REQ pins are:
- ND_ACK_REQ_EXCHANGE_GR1 - Used for ACK1 and REQ1 pins.
- ND_ACK_REQ_EXCHANGE_GR2 - Used for ACK2 and REQ2 pins.
(Note: See Figure C-1 on page 99 of the NI 653X User Manual for a pin diagram). The last input parameter,
infoValue, is the new value assigned to the
infoType parameter. The two options associated with the ACK and REQ exchange attribute are:
- ND_ON which enables the ACK and REQ pin exchange.
- ND_OFF which disables the ACK and REQ exchange.
If Measurement and Automation Explorer assigns your data acquisition card as Device 1 and the ACK1 and REQ1 pins are being used, the source code would appear as
status = Set_DAQ_Device_Info (1, ND_ACK_REQ_EXCHANGE_GR1, ND_ON).
Related Links: NI 653X User Manual
KnowledgeBase 35KDQAKD: How Are the ACK and REQ Lines Controlled on the 653x DIO Devices?
KnowledgeBase 3LDGM4S9: How Do I Connect Two 653x's?
Attachments: 
Report Date: 10/10/2005
Last Updated: 10/12/2005
Document ID: 3Q97846S
