I've finally made a expansion slot card for my sbc, to which i would connect the crtc module and 4 other expansion slots. For now the connectors are made from just one row of pins, and it is a bit wobbly... Now i am worried that if a bad contact occurs there might come to a bus error, and halt the 6502...
Also i wonder if the NMOS 6502 can handle so much stuff attached to the bus, or it would need buffering/amplification(expansion slot length 16cm).
I've seen lots of sbc expansion boards, in various projects, so if you could discuss some of this issues?

It's difficult to make expansion buses like this behave well at higher speeds, but the NMOS 6502 wasn't fast anyway so you're probably fine. 30+ years ago they usually put bus transcievers in 6502 computers, but that was partly because of all the 74LS loads. CMOS (like 74HC) loads are mostly like a multi-megohm resistor load with a few pF in parallel. The CMOS 6502's however can drive much, much more current than the NMOS ones could (even if the specifications are very modest).

And what about wobbly connectors?

Every system I've seen with expansion cards relied one one of two methods to provide secure connections:

1) A vertical card with at least one screw hole per card to secure the card in place. Think PCI cards here, where you have outward facing brackets with a screw on top. Some might say that NuBus slots were secure enough to support a self-standing card of some weight, but even NuBus cards found in the Mac-II machines had plates and mounting screws.

2) A horizontal edge connector which mates with a female slot soldered to a similarly horizontally mounted PCB on the peripheral. The idea being that the peripheral is heavy enough that resting on a desk surface would provide a relatively vibration-free and secure connection to the motherboard. Think Amiga 500 expansion slot.

Well, i only have single row pin headers and ordinary experimental boards... So i will have to invent something...
The PDP11 has a nice system, but my boards are all different in size...

I'm not familiar with the PDP-11 expansion hardware; can you link to a few sites that describes it in some detail?

The PDP-11 used a card frame with cards with edge connectors at the rear. There was no card locking screw or mechanism, just ejector handles to make it easier to pull the cards out. Check out the UNIBUS and Q-BUS entries on Wikipedia for more info.

_________________
Shift to the left,
Shift to the right,
Mask in, Mask Out,
BYTE! BYTE! BYTE!

Any useful small scale ideas?

There's the Modular SBC

How about using two sets of single row connectors; one at each end of the board?

Toshi