HP E1429A manual VME Bus Data Transfers, Locating the Data Register

VME Bus Data Transfers

Locating the Data Register

Another method of transferring readings to the VME (VXI data transfer) bus is with the digitizer’s VINStrument (Virtual INStrument) subsystem and accessing the digitizer’s data register. This method, which combines message-based (SCPI) programming and reading the data register directly, is faster than the previous methods (READ?, FETCh?, DIAGNostic:UPLoad:ADDRess?) in that readings can be retrieved from the A/D converter or from memory in the A/D’s packed data format.

There are two modes of VME data transfers: real-time and post measurement. In a real-time data transfer, reading the digitizer’s data register triggers a measurement and returns the A/D reading to the VME bus in the same measurement cycle. In a post measurement data transfer, reading the register transfers a A/D reading from digitizer memory to the VME bus.

How to select the transfer mode is covered in the section "Setting the VME bus Transfer Mode". Examples of VME bus data transfers are listed in Chapter 2 - "Using the Digitizer".

Access to the digitizer’s data register is through its address which is mapped into A24 address space. At power-on, the system resource manager reads the digitizer’s device type register (in A16 address space) to determine the amount of A24 memory the digitizer needs (which is 4096 bytes). The resource manager allocates a block of A24 memory for the digitizer and writes the A24 base (starting) address into the digitizer’s offset register (also in A16 space).

Figure 3-12 is an example of how the digitizer registers are mapped into A16 and A24 address space. Appendix C contains additional register programming information.

146 Understanding the HP E1429 Digitizer Chapter 3