Modifying microcode

[Jon Elson]

On 06/02/2018 03:33 PM, Antonio Carlini via cctech wrote:
> On 02/06/18 15:17, allison via cctech wrote:
>>
>> It was my understanding from using the 730 that there was 
>> limited
>> (really limited) microcode
>> enough to load the WCS as the tu58 was a serial device 
>> (standard tu58)
>> and the 730 had to
>> unpack and stuff the WCS.  You need little to do that but 
>> far from even
>> PDP11 instruction set.
>> The Microcode was loaded was the "what made it a VAX stuff".
>>
>> Allison
>>
>
> Well something has to load the ucode but whether that's a 
> fixed part of ucode itself or whether
> it's a hardware state machine (or something) that feeds 
> the loaded ucode into the appropriate
> RAM, I don't know. I've never delved that deeply into the 
> relevant FMP sets.
>
Actually, the 8085 could load a small bootloader from 8085 
ROM to the 730 microcode.  That would be the most logical 
way to do it, assuming the microcode bootloader was really 
small.

The IBM 360/25 had all microcode in the top 16K of main core 
memory, and the emulator of your choice could be loaded from 
binary punch cards.  The microcode bootloader was 
hand-loaded through the front panel switches, and occupied 
16 16-bit words.

Jon