Monitor/OS taking shape, EPROM emulator 5

Monitor/OS taking shape, EPROM emulator

Sep

14

2011

I have just returned from a two and a half week training combined with short vacation. I haven’t posted for a while but the project is well alive and it will regain momentum now when I am back home. Immediate plans are to complete the Monitor/OS with a little help of a nice gadget described ...
read more →

Software

Assembler and instruction set update 2

Jul

31

2011

I am slowly progressing on my simplistic OS/Monitor development. It is only a little fun, mainly because I do not have a functional simulator (i.e. emulator) of the computer and I have to test every bit of assembly code on real hardware. For that I have to constantly switch from Linux (where my development toolchain ...
read more →

Design - ISA · Software

More bugs

More bugs

Jun

14

2011

Recent exercises with UART revealed two interesting bugs in my design. Both problems were resolved and I am documenting them here for dairy keeping. Implicit memory reads It is something I have discovered only now, playing with real devices attached to the CPU’s expansion bus. The problem is related to side effects of implicitly reading ...
read more →

Design · Design - control

It talks! 5

It talks!

May

28

2011

I now have a computer with support for RS-232 serial communications. Since my last post I managed to build and preliminarily test the new device card with two 16550 UART chips. Somehow it makes me very excited, because for the first time I will be able to communicate with my system by means of keyboard ...
read more →

Construction

UARTs board draft schematics

UARTs board draft schematics

May

7

2011

I completed the initial revision of UARTs board schematics last night. Both 16550 UART chips and MAX232 level converters were new to me, so the task took several hours. Unlike with simple TTL chips, this time I really had to study the datasheets carefully to understand what all those pins do. I am only going ...
read more →

Design - I/O

Serial ports (based on 16550D UARTs) 5

Serial ports (based on 16550D UARTs)

May

2

2011

With the CPU completed, it is time to think of an I/O to be able to play with the system somewhat more interactively than by plugging EPROM chips in and out and attaching logic probes to data and memory buses. At first, my plan was to build a PS/2 keyboard controller (input) and a rudimentary ...
read more →

Design - I/O