XT/370 microcode

[Camiel Vanderhoeven]

On 3/15/18, 9:29 AM, "cctech on behalf of Veit, Holger via cctech" <cctech-bounces at classiccmp.org on behalf of cctech at classiccmp.org> wrote:

    You might look up Nick Tredennick's book "Microprocessor Logic Design: 
    The Flowchart Method" which is sold at Amazon for an obscene price - but 
    maybe some university library has a copy. It's focus is on a methodology 
    for designing microcode, and it uses the design of the single chip 370 
    to explain it. I suppose it was a PhD thesis.
    
    The main point is that the 370 is NOT an 68000 with a different 
    microcode; instead it is said that it implements the bus interface of 
    the 68K in order to interface easily with existing peripherals (rather 
    than reinventing the wheel). The internal data paths and register sets 
    may be similar between the 68K and the 370 (actually it is quite 
    possible that at Motorola they were aware of IBM mainframe 
    architectures...) but that's all likely. The control unit design 
    described in the book was completely redesigned for the purpose of 
    describing the proposed methodology.
    
    Holger

There are two distinct products (well, one product and one project that never made it onto a product) here that get confused. First, the XT/370. This card uses a 68000 with modified firmware (nick was one of the Motorola engineers helping implement this for IBM), as well as a modified 8087, and a stock 68000. Later, Nick left Motorola and came to work at IBM on the Micro/370. The Micro/370 is the 370 on a single chip, and it uses the 68000 bus, but is otherwise different from it. A good writeup of the story can be found here: http://www.cpushack.com/2013/03/22/cpu-of-the-day-ibm-micro-370/

Camiel