Nascom News­let­ter

Testing is quite simple, I found. It’s a matter of fitting the WAIT – GATE with all the WAITs (M1 and R/W) in operation, giving a normal and average cursor flash rate. This is followed by setting to no WAITs, which gives a noticeable change of cursor rate. A further test of M1 WAITs only, gives an increase in cursor rate, but lees noticeable. (In almost all systems the NAS-SYS ROM and workspace RAM will work without WAITs). Any poor connections of the wire wrap sockets will show up as faults in other sections of the Nascom circuit. These include the RESET switch, single step logic, PIO, and serial interface. The manual explains this, and these functions should be watched during first operations:

TABLE 1. SWITCH DATA

TABLE 2. MEMORY DEVICE TIMING

Using the above tables, the latter section of the manual explains how the switches in Table 1 are used to provide each ROM and RAM speed in Table 2. Switches 1 and 2 are set for ROM; 3 and 4 for RAM. If an access tine of < 400ns and > 275ns is required for ROM and < 275ns for RAM, the switches should be set:

The main idea behind the WAIT – GATE, says the manual, is:

“In most systems only some memory access cycles actually need WAIT states. The WATT – GATE circuit provides a flexible means of controlling WAIT states so that the number of unnecessary WAIT states is minimised. This can result in a considerable increase in C.P.U. speed.....”

This I must agree with, when you consider that by far the most frequently used operations are the reading and writing of the memory, both ROM and RAM.