Daryl's Computer Hobby Page
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First and foremost, I offer this board "AS-IS", with no
guarantee that it is without defects or flaws. So, use
it at your own risk! Having said that, I plan to buy at
least two myself, and have worked very hard to ensure
everything is covered. I will help with whatever
"problems" arise, but do not promise anything!
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First, see the parts placement picture for component locations and values.

The power busses are at least .030 wide and are rated for 1 amp (according to ExpressPCB), be careful not to overload them or you may melt traces.   Be especially careful to avoid shorts or excessive loads from your devices plugged into the IO ports.

If you look closely at the board layout, you'll see several extra pads, especially around the 65C02.   I have tried to make the board as versatile as possible.   Note especially that if the 65C02 Pin 1 is to be grounded, you'll need to install the strap to the left of the TTL Osc.   This allows for use of the W65SC02S, which has a VPB output on pin 1. Also, there are pads for MLB, RDY, SYNC, BE, & SOB.   Hopefully these will allow for special uses.

I have made the IO completely strap-selective.   You can select/deselect both 6522s and the 6551.   You can connect their IRQ outputs to NMI, IRQ, or leave them open.   I've added pads for diodes in the IRQ's of all three IO chips. If you don't need to use a diode, you can simply solder a strap across the pads.   The diodes would be needed for totem-pole IRQ's, which cannot be wire-OR'ed together.

For the 6551, you can choose between the DTR/DSR, RTS/CTS, & DCD handshake connections to the MAX-232.   You can also select the appropriate pins from the MAX232 to the 10 pin RS-232 connector.   See the "options.gif" file for stapping examples.   Use a 22pF capacitor next to the 1.8432MHz crystal.

The four 6522 Ports are wired for power, gnd, 8 bits + 2 handshake.   I was unable to re-wire the power as to prevent damage by reverse connection, but I did add one pad to the right of the +5 pins, so if you have room, you can use a 16 pin socket and key the hole to prevent reversals.

RP-2 is optional and is only needed if you want to be able to leave a 6522 plugged in but want to disable it by removing the CS strap.   RP-2 would provide the necessary pull-up for the CS pins.

I've also added straps to support both 28256 EEPROM and 27256 EPROM.   See "options2.gif" for strapping examples.

I'll be including the expressPBC data file and Eagle Lite schematic files for this board to the "Download" tab soon.

Also, once tested, I'll include a copy of my simple OS for the SBC-2.

All info provided "as-is" and is Copyright 2002.