*** Use the following information at your own risk.   I offer no guarantee that this information is without defects or design flaws.

"SBC-2 v2.5" is a slightly midified version of the 2.3 board. It includes space for a 1 MHz 65c02, 32K of static RAM, and 32k of EEPROM.  It also has two 65C22 Versatile Interface Adapters (VIA) and one 65c51 Asynchronous Interface Adapter.  The modifications include addition of a 7805 voltage regulator, more space around the EEPROM pads to allow for a ZIF socket, reconfiguration of the Serial port Connector, and addition of all address lines to the expansion connector.   There are eight 16-byte address blocks decoded for I/O, the on-board I/O chips use three of these (their CS pins are connected via jumpers and may be disabled).  There are 5 unused address blocks available for more I/O through the expansion port.  In addition, by adding one 74LS138, you may decode an additional eight 16-byte I/O addresses.  All 3 I/O chips have jumper-selected interrupt connections to either the IRQ or NMI on the 65C02.   I've included some user-selectable options to the serial port and also added a better reset circuit.   You can now select the handshake signals that you want to place on the port, like CTS/RTS or DSR/DTR or DCD.   You can also use a capacitor for a simple power-on reset circuit or use a DS-1813 or equivalent reset device.   This will provide a cleaner, more reliable reset pulse to all of the IC's.   I also included jumpers to allow a choice of EPROM/EEPROM's, added pads for unused 65C02 pins, and the 6551 RX Clk.

A support file which included ExpressPCB schematic and board layout along with GIF image files can be downloaded here ->

I have developed a monitor program with basic INPUT/OUTPUT support, a mini-assembler, and also Lee Davison's Enhanced-BASIC Interpreter.  This will make the board a very practical SBC!

More info on the OS can be found here ->SBC-2 OS

NEW! - I have created a CC65 target for the SBC-2. You can now write your EEPROM-based programs using CC65 and copy them to your EEPROM. The support files are located here -> CC65 for SBC-2

The Memory map is as follows:

0000-7EFF - RAM (32K minus 256 bytes)
7F00-7F4F - Five unused decoded I/O Blocks (16 bytes each)
7F50-7F5F - VIA1 (16 bytes)
7F60-7F6F - VIA2 (16 bytes)
7F70-7F7F - 65C51 (16 bytes)
7F80-7FFF - undecoded I/O blocks (128 bytes)
8000-FFFF - EEPROM (32K)


All info provided "as-is" and is Copyright 2020.