| Re: Question ISA BUS clock [message #6201 is a reply to message #6200] |
Tue, 02 April 2019 00:07   |
32768
Messages: 4
Registered: October 2018
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Junior Member |
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Sergey wrote on Mon, 01 April 2019 12:01It would help to describe what are you trying to debug 
well, our micro8088 don't have a RTC, mean while more and more I realize that I like making small and simple bios extensions, so I'm thinking to make a board with:
- one RTC, basically an adaptation of smbaker RTC design (only the rtc part) http://www.smbaker.com/8-bit-isa-diskonchip-rtc-board just I will be adapted for https://www.tme.com/us/en-us/details/ds12887+/rtc-circuits/m axim-integrated/ or https://www.tme.com/us/en-us/details/ds12887a+/rtc-circuits/ maxim-integrated/ (this is what I can find locally ready to buy)
- two bios extensions, again copy paste from http://www.malinov.com/Home/sergeys-projects/isa-fdc-and-uar t (only the Bios extension block)
This two parts are tried and tested, don't even need to worry about.
The reason to my madness is this: https://en.wikipedia.org/wiki/DCF77 a radio signal for clocks (at the middle of the wikipage is the description of the signal), on the market this modules exist https://www.pollin.de/p/dcf-empfangsmodul-dcf1-810054 so I'm thinking... what if I can make a port, with a microcontroller to read that dcf77 module, synchronize his internal timer, and when I read the port, lets just consider last four address lines, A0(1) put seconds on the databus, A1(2) minutes,A1A0(3)hour... etc.
Thing is, with DCF77 because is a long wave, it takes a long time to have a full transmission, even longer for a valid transmission without corruption, so only when I have a valid transmission I can set microcontroller internal timer to the current hour, min, second, plus store the year/month/day in some variables.
What I'm trying to measure is, if the microcontroller is fast enough to put data on the bus, when:
- interrupt from 74LS688 CS is low (A19-A5)
- differentiate A4-A0 to know what data I read
- maybe another interrupt for ALE?
- interrupt for #IOR (B14)?
- other flags I should be worry about?
And only when all conditions are true, microcontroller should put the data. Problem is... I don't think is fast enough even for 4.77MHz, not to mention if I put the board in a 268 or 386 at much faster speeds.
At the moment I'm at the stage of just measuring and throwing ideas how I can build such a port. Advices are welcome.
Edited: also need to set the data 0xFF when I read the port but I don't have yet a valid read from radio signal, no matter if I want read hour/year/second. Maybe others errors will be need it along the way.
[Updated on: Wed, 03 April 2019 03:56] Report message to a moderator |
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