NI PXIe-6674T Vector network analyzer

If the BAU signal is inactive (S 301), the system initialization distinguishes between BOOT and RUN, depending on the switch setting. If BOOT has been selected, the system program is first transferred from the system diskette to the write–protected (for the user) system RAM, and the system program is then started. If RUN has been selected, the system program is started directly (S 301).

The first faulty or missing memory location is marked as memory end. The central processor goes to STOP and the red CPU LED lights up if the system detects a memory size < 64 kB. The system program command BT,STAT:@ displays the memory size determined for the user by the microprogram.

Microprogram initialization 

The microprogram of the central processor first performs a memory test. The microprogram performs a byte parity generation for the system RAM which is stored in the parity RAM associated with the system RAM. The system then performs an error–free reading check. The first faulty or missing memory location is marked as memory end. The central processor goes to STOP and the red CPU LED lights up if the system detects a memory size < 64 kB. In the user RAM, the microprogram checks every address for data and access errors (byte parity or memory error) using two bits patterns. When the BAU signal is active, the whole user memory contents is deleted and, if the memory is buffered, the original content is rewritten into the memory. At the same time, the new parity bit in the parity memory is generated.

CPU monitoring

 Once microprogram initialization has been terminated, each access to the system or user RAM during program execution is monitored for parity and access. This facilitates recognition of new system RAM failures or read errors (byte parity) during normal operation. A flag “NNN” (illegal instruction) is set if one of these faults occurs when an instruction is read. Selective reactions are performed during data access. Special handling of the processing level currently active is started when these monitoring messages occur during program execution. The microprogram branches to the system initialization level and the initialization program attempts a restart if one of these messages appears during special handling. If new flags appear, initialization is first of all repeated during the special handling of the flags. If, during this special handling, a further fault occurs in the initialization level, the microprocessor sets the central processor to STOP.

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