Nascom Newsletter |
Volume 3 · Numbers 5 & 6 · June 1984 |
| Page 48 of 69 |
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On completing the wiring, I suggest powering up the emulator board without any chips inserted. The supply pins may be checked at this stage at each IC socket for correct polarity. The chips may then be inserted one at a time whilst monitoring supply current for excessive drain.
A cable may be made up with a 16 pin header to connect to SKT 1 at one end and an appropriate connector for ports A and B of the Nascom, in my case a Canon type. The connection diagram shows the pin numbers for direct connection to the two 16 pin headers on a Nascom 1. Finally, you can put the whole thing in a box if you want to be slick!
Being simple-minded, I tend to use one extremely basic loader routine which transfers a 2K block of RAM from the Nascom to the emulator. The routine is relocatable but resides in ROM at address D42F which happens to be convenient in my system. The routine is so basic that, as it stands, the data to be transferred must reside at address 4000H in the Nascom memory. It would be easy enough to pick up an extra parameter with Nas-Sys E command to improve this…
The following table gives the functions of the emulator control lines, driven by the lower five bits of Port A, which is configured as an output port at all times. Port B is used for data transfer and must be configured for output only when leading data, otherwise it is left set up for input.
| Port A bit | Name | Function |
|---|---|---|
| 0 | SWITCH | Enables access by host when HIGH |
| 1 | ADCLK | A low to high transition on this line advances IC 1’s count by one |
| 2 | ADRES | a high level on this line resets IC 1 |
| 3 | /WE | Write Enable for the RAM, active low |
| 4 | CS | Chip Select for RAM. Note active HIGH |
Port B bits 0 to 7 are connected to data bits 0 to 7 of the emulator respectively.
To load the emulator, the program must generate the following sequence:–
| Page 48 of 69 |
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