|
|
Post by gauze on Jul 15, 2013 16:40:42 GMT -5
I have been doing some independent electronics study and I have been gawking at some vectrex schematics and have been trying to figure out how the memory mapped io stuff works. checking www.playvectrex.com/designit/chrissalo/memorymap.htm I can see the memory map and in www.playvectrex.com/designit/chrissalo/appendixb.htm I see some specific memory locations where you can read from various IC ports, electrically how are these connected exactly I guess is my question? This might be too broad of a CS question I realize. I don't see any chips to encode/decode addresses and route them so I'm a little stuck. Has anyone does a step by step flow chart or whatever of what happens when a vectrex is powered on/reset btw? Might be helpful for troubleshooting. |
|
|
|
Post by gauze on Jul 16, 2013 6:50:37 GMT -5
never mind it doesn't have a (dedicated) decoder it's done via the 2 74xx TTL chips  |
|
|
|
Post by sj on Jul 16, 2013 9:06:54 GMT -5
At this point in my membership here I would just like to say I got a very low score in my electronics exam circa 1979.
I thought Vectrex's were powered by magic and wizardry.
ps. I was very good at woodwork.
|
|
|
|
Post by gauze on Jul 16, 2013 23:01:41 GMT -5
I built a guitar last year. it only took me 3 years to finish it.
|
|
|
|
Post by sj on Jul 17, 2013 9:47:34 GMT -5
That's quite an undertaking.
Last week I built a small ramp out of bit a scrap timber to enable the frogs in my pond easy access/egress. That took me about 3 minutes.
|
|
|
|
Post by kokovec on Jul 17, 2013 17:40:07 GMT -5
The Vectrex decodes the address bus to select between the various chips that hang off the bus (including the cart ROM). I used this to my advantage while working on my 3D adapter. I've attached my PSOC UDB design that I implemented. It's an early version as I had to refine the design to fine tune the system timing characteristics. The 3D adapter actually uses 2 separate 32K RAM chips. The first chip acts as a cart ROM but the second chip is seen by the Vectrex as 17K of expanded RAM. The balance of the RAM on the second chip is used by the adapter itself. The adapter also turned the Vectrex into an FTP client so it could download binary ROMS from an FTP server. The Vectrex is very flexible in it's design. Top Design 08_21_2011.pdf (195.5 KB) |
|
|
|
Post by gauze on Jul 19, 2013 23:07:33 GMT -5
ok then there is something I am not getting. let me run you through my mental process, then you explain how I am a dummy.
I check the Memory map and for example it says E000 is start of internal ROM so I quickly do some binary translation:
1110 0000 0000 0000
reverse that and that should be the states of my pins on the address bus numbered from 0-15
so now I look at the schematic, pin A15 and A14 connect to a NOR gate, they are both hi so the output is 0 that goes to pin 22 on the ROM which is Output enable ... so basically I can't read from the ROM now?
I gotta be missing something here ...
|
|
|
|
Post by gauze on Jul 20, 2013 11:32:37 GMT -5
er NAND not NOR
|
|
|
|
Post by gauze on Jul 21, 2013 13:58:03 GMT -5
argh I just ran across a mention of the ROM (2764) requiring TTL Low on those pins to enable reading, I assumed high was what they wanted, that apparently is what the line over the top means in the ic pinout and schematic, NOT/false/ttl low. Learning from my mistakes here.
|
|
|
|
Post by kokovec on Jul 26, 2013 13:17:01 GMT -5
Yes, typically the WE, CE, CS, OE, and Write lines are active low. As is the RESET line.
It comes in handy for address decoding.
|
|
|
|
Post by gauze on Jul 26, 2013 13:35:44 GMT -5
I'm learning a little everyday here, the address decoding part I "got" but this solidified it more for me.
|
|
|
|
Post by sj on Jul 28, 2013 12:30:23 GMT -5
I love this thread. My guess is only two people know what the f*** it all means. Kokovec and gauze I salute you.
If you need any help getting the frogs out of your ponds drop me a pm.
|
|
|
|
Post by gliptitude on Jul 28, 2013 20:46:15 GMT -5
I love this thread. My guess is only two people know what the f*** it all means. I wish I was one of those people. I think with rigorous study I could have some comprehension, but my impression is that it is like so many other things - it's one thing to read and understand or to enact through imitation, but it is quite a different thing to achieve an INTUITION that is native to those who really know what it means and how it works. I don't think it's practical to aim for this if you are also focused to the same extent on other dramatically different studies... If I was a vampire, with hundreds of years in my prime on this earth, I would devote a decade or two to electronics and programming, (and another to carpentry, another to painting, another to filmmaking, baseball playing, medicine, architecture, romantic exploits etc.) ... As it is though for most people, it seems necessary to choose between these things. |
|
|
|
Post by gauze on Jul 28, 2013 22:05:02 GMT -5
I am just learning but I took some electronics courses years ago, program a bit, and figure nothing works by magic so you just have to put some time in to learn it.
|
|
|
|
Post by sj on Jul 29, 2013 8:12:32 GMT -5
Ok Glip. You stick to your projects. If I was a vampire I'd be happy biting the necks of beautiful women. |
|
