ClausB

Is your design based on a microcontroller? Here's an OTS customizable controller, though rather pricey at $99: http://www.sprintek.... User Guide.pdf

This deserves a bump. Just came across this interview. It's a must-read.

I looked for CHRST because I wanted to find a reason for why they put the HMxx offset in the high nybble and not the low. In the thread "Racing the Beam" supercat asked: "Was the decision to have HMxx latch D4-D7 really predicted upon 'ease of coding', or hardware layout considerations? In what anticipated scenario would it ease coding?" and Decuir answered: "for many moving objects in the Combat display (the original target game) the motion vector for the tank had a 4 bit horizontal and a 4 bit vertical component. We used the high nibble for horizontal; I don't remember why. Probably because we could mask off the top 4 bits to add to the current vertical position value (a memory byte) without having to shift anything." In CHRST, the division by 15 is done by repeated subtractions and the remainder ends up in the low nybble. It has to be shifted before writing to HMPx. Another way to divide by 15 is to multiply by 1/15, (0.000100010001 binary), using shifts and adds. In that case the remainder ends up in the high nybble and needs no shifting for HMPx. So I was wondering whether Decuir did CHRST that way, but no.

I found it in Video Olympics by Decuir: It starts at F445 and the BRK calls the routine at F438. It ends at F45E with an RTS.

From the thread "Racing the Beam": Has anyone ever posted the source code for the CHRST subroutine? Or a disassembly of its use in an early Atari game? In his presentation (http://www.atariarch...v/CGEXPO00.html) Mr. Decuir implies it is used in COMBAT but it does not appear in the "definitive" disassembly (http://www.atariage...._asm/index.html).

Has anyone ever posted the source code for the CHRST subroutine? Or a disassembly of its use in an early Atari game? In his presentation (http://www.atariarch...v/CGEXPO00.html) Mr. Decuir implies it is used in COMBAT but it does not appear in the "definitive" disassembly (http://www.atariage...._asm/index.html).

According to the Atari 5200 Service Manual, there were two different versions of the four port model, as far as the circuit board goes.

Neither the expansion port nor the cartridge port, by itself, is really RAM capable. The expansion port lacks enough address lines - you could bank switch but only with very small banks. The cart port lacks write and timing signals, though you could kludge a RAM as was done for the 2600. Together, the two ports would support a decent RAM upgrade. Put the RAM in a cartridge and run a small cable back to the expansion port. With 16K bank switching, a la 130XE, you could add as much RAM as you need, without internal mods, as Rybags said.

I've thought about it some too. The 800 uses PIA signal CB2 to generate -COMMAND and it uses SKCTL mode 2 to transmit data and 1 to receive. The 5200 has no PIA, of course, but if we use SKCTL mode 6 to transmit, then data gets clocked out at one rate and we can output a signal at a different rate on CLOCKIN. If we wire CLOCKIN to the drive's -COMMAND and program it to generate the one long pulse, then we get all we need without adding a latch nor any active circuitry. Haven't tried it but I think it should work. As you said we need a ROM cart for the SIO program and a mini-DOS. It could be a read-only DOS just for loading 16K games into RAM, or it could have some write capability for saving game states or scores. And like you said the cart could also contain RAM. We would have to wire two signals (R/W and Ph1) from the expansion port to the cart to support the RAM. 16K or 24K of SRAM would give lots of room for bigger games. Maybe we don't need it today, but it could have been something back then.

Has anyone ever done an SIO disk interface for the 5200? Seems it could have been cheaper back in the day to distribute 5200 games on floppy than in carts, though the up-front cost of an Atari drive might have put off potential customers. Or were there just not enough 5200s out there for the software houses of the day to bother?

Congrats! When you open your 400s don't forget to reseat the chips. That is, gently pry each chip part way out of its socket from both ends and push it back in. Use a small thin blade screwdriver. That has fixed my 400s several times.

XEGS console only, filthy, broken, but cheap. No sockets - will be hard to troubleshoot. Most of its chips have 1987 datecode except ANTIC and GTIA which are from 1983. They must have had piles of old stock to use up.

See this post:http://www.atariage....ost__p__1481893

Not PB0 and PB7. Those bits have the normal XL functions. The upgrade uses PB2 through PB6 so you would set those bits to access the RAM under $C000-$FFFF at $4000-$7FFF.

The Buchholz/RAMbo/Wizztronics 256K mod allows access to those 2K.

No, it uses 4K select lines where the production cart slots have 8K selects. It could only address 8K of ROM at most.

Notice that the original cart connector had only 24 pins and the cart held 2 4K ROMs. That's 12 address lines, 8 data, 2 power, and 2 chip selects. No R/W line nor I/O select, so it was for ROM only, no RAM nor I/O, just like the 2600. Glad they fixed that!

Thanks! Our sister team took 2nd last year but we flopped. We're ready now though. Go VEX Raptors! Any AtariAgers in Anaheim in two weeks? Drop in and watch.

The LEM project is not dead, just on hold. My spare time is dominated by coaching my VEX Robotics team. For the second year we won a local tourney and are preparing for the World Tournament. That makes for a long season - August thru April. And summer is flying season around here. My Atari activities have been limited to collecting and repairing - an 800, three 400s, a 5200, an Apple //c, several old TI and HP programmable calculators, and an XEGS on the way.

The LEM project is not dead, just on hold. My spare time is dominated by coaching my VEX Robotics team. For the second year we won a local tourney and are preparing for the World Tournament. That makes for a long season - August thru April. And summer is flying season around here. My Atari activities have been limited to collecting and repairing - an 800, three 400s, a 5200, a 600XL, an Apple //c, several old TI and HP programmable calculators, and an XEGS on the way.

Or just learn to appreciate the 400 for what it is. It has the best membrane keyboard of any. It does not work well to poke at the keys and that hurts the fingertips anyway. What I've always done is to lightly feel each key with the raised edges and then push off and hear the speaker click. It's fast enough with a little practice. If you do replace the membrane keyboard, please don't toss it. Pass it on to someone who wants it. Maybe you could even find someone with an aftermarket keyboard who wants to restore his 400 and trade?

Mine had ounces of memory, about 1/4K user RAM. Bought it senior year of high school with my summer job money. Loved it! That's very cool The TI SR-56 came with a book of programs to key in, including a lunar landing game which I modified. Then I wrote some astronomy programs and a few more games, including tic-tac-toe. I also translated an HP25 program from Popular Electronics called Space Flight by Paul Lutus. Great fun!

Cleaned, reseated, tested, works!

Mine had ounces of memory, about 1/4K user RAM. Bought it senior year of high school with my summer job money. Loved it!

2 more 400s for $5! One is fairly clean and worked after reseating the chips. It has the Sally CPU board. The other is filthy and not yet tested.