2015-05-04 04:15 UTC
Even though the MC3 is in its core a Motorola 68xx design it can use 65xx parts. The bus and timings are the same. I initially planed on building an I/O board around the 6321 PIA but ended up trying out the feature packed 6522 VIA instead. The 6522 is actually still being manufactured by WDC! The 6522 is familiar to anyone working with the 6502 or MOS/Commodore machines. In general it's a souped up 6821 with two timers and a shift register. The 6522 consumes more address space than the 6821 but each register can be directly addressed, thus making it faster for certain tasks. It requires four address pins instead of only two but for me that's a perfect match since my I/O boards each have 4 address lines making it a 1:1 match. Connecting the 6522 to the MC3 20-pin I/O expansion bus require no extra circuitry. It's only a matter of connecting the corresponding pins together. Since there is no IRQ line on the I/O bus I will have to settle for polling the 6522. Thank you Douglas Beattie for sharing your Eagle 65xx library. The 40-pin chip is a tight fit on the small 20-pin I/O board but it worked. For now there are no connectors for the 6522 ports. Not much space left but I should be able to mount a suitable connector at the top of the board. I really like how the 6522 engineers have separated the bus pins and the I/O pins to different sides of the chip.
by gerardo pintor alarcon 2017-02-28 22:50 UTC
You can support me with an example diagram and more information.
by JOHNNY QUEST 2021-02-21 05:46 UTC
Helllo Daniel: Nice articles you've posted. I've recently decided to design a MC68B09/HD63B09 based SBC. Fairly simple design with 32KB of SRAM and 30K of UV-E/EPROM (lower 2KB address space is dedicated for I/O). I'm using the HD63B50 and an AT16V8 PLD for the decoding. The 6x09 is running at 7.3728MHz, which gives an E clock of 1.8432MHz for the HD63B50 and a baud rate of 115.2kbaud (or 28.8kbaud). I have several 6821's but also found I also had two 6522's (OEM is COMMADORE BUSINESS MACHINES) in my archive collection. Its nice to have the timers and serial interface of the 6522 and feed the 6809's NMI interrupt for system timing. I allowed a single 24-pin I/O header to provide 3 additional I/O decodes and the lower 4 address lines. Your CF card interface looks simple and clean but I have not looked into obtaining any. I plan to post the build as I go along. I've got some posts on some other "vintage" single-board computers, including the INS8073 w/ NCS NIBL BASIC interpreter from the early 80's. Its a wire-wrap build of mine from that era (I was like 19 years of age then!). If you are interested, the link is at http://8073sbc.wordpress.com. The other SBC posts can be accessed from the links at the top of the page. Q: do you know where I can get the source code for FLEX-09, which is the 6809 version of the FLEX OS? Peace and blessings, Johnny