UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

JohnBHanson · 12th Jan 2020, 10:10 pm

Running in the top slot will be fine - my warning does not really apply to the MFB system but was to any other readers that run other systems.

Now for some useful infomation to you. The processor reset on the SVC card is not connected to the backplane reset. The SVC reset can come from two sources the first being a power up and the second being an in/out instruction to port 0b3h.

The fact that pressing the reset button on the CPU card causes the SVC card to reset means that the GM813 is executing the instruction to reset the SVC card. This means that it can perform I/O cycles on the backplane and also execute code from the eeprom.

This is a major finding that will help in your fault diagnosis.

The next feature I would check would be the RAM on the GM813 or possibly the memory mapping hardware on the GM813- the startup sequence is covered in the GM813 manual.

12th Jan 2020, 10:10 pm	#308
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Gemini 80-Bus System Running in the top slot will be fine - my warning does not really apply to the MFB system but was to any other readers that run other systems. Now for some useful infomation to you. The processor reset on the SVC card is not connected to the backplane reset. The SVC reset can come from two sources the first being a power up and the second being an in/out instruction to port 0b3h. The fact that pressing the reset button on the CPU card causes the SVC card to reset means that the GM813 is executing the instruction to reset the SVC card. This means that it can perform I/O cycles on the backplane and also execute code from the eeprom. This is a major finding that will help in your fault diagnosis. The next feature I would check would be the RAM on the GM813 or possibly the memory mapping hardware on the GM813- the startup sequence is covered in the GM813 manual.