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Home Page 65C02 SBC Backplane Floppy Disk IF


What is it?

This is a Printed Circuit board for a 32 row by 64 character VDU. It is designed for 2k x 8 of Sram and a 2k x 8 EPROM for a character generator.

Why did you make it?

I have built many 65C02 projects and wanted a generic VDU I could attach easily. This PCB, when populated, will attach to any 65C02 SBC as the Databus is buffered and the address location can be decoded as any 2k in the 64K window,

What makes it special?

You cannot buy this interface elsewhere so I had to research and design a PCB I could use.

Screenshot of CEGMON dumped to VDU Memory

BOM for 32 X 64 char 2kB Ram VDU PCB



IC1   74LS245 Octal Bus Transceiver.
IC2,IC3,IC4   74LS157 Quad 2 to 1 Data Selector.
IC5,IC6,IC7   74LS393  Dual 4 bit binary counter.
IC8   74LS139 Dual 2 line to 4 line decoder.
IC9,IC10   74123 Dual retriggerable monostable multivibrator * See Note 1).
IC11   74LS165 8-bit parallel-load serial-out Shift Register.
IC12   2716 2K x 8 Eprom or equivalent.
IC13,IC14   74LS02 Quad 2-Input NOR Gate.
IC15   74LS04 Hex Inverter.
IC16   74LS08 Quad 2 input AND Gates.
IC17   74LS00 Quad 2 input NAND Gates.
IC18   5516     2K x 8 Sram or equivalent.
C1 0.22uF (224)  
C2 0.022uF (223)  
C3 120pF (121)  
C4 220pF (221)  
C5,C6,C7,C8 0.1uF (104)  
C9 1000pF (102)  
C10 680pF (681)  
C11,C12,C13,C14 0.1uF (104)  
C15,C16,C17,C18 0.1uF (104)  
R1 4.7k    
R2 22k    
R3 390    
R4 220    
R5 150    
R6 620    
R7 47k VR    
R8 680    
R9 33k    
R10 N/A    
R11 4.7k    
R12 15k    
D1 IN4148    
OG1 12MhZ Oscillator (14 pin size)
J1&J2 2x18 way 90 degree pins
J3 8 x 2 pin    
J4 RCA Connector  
J5 3 way A15 selector  
PCB Layout
VDU Address Decoding
Resistor Location and Values
CCT Diagram
I sell on Tindie
(c) 2021,2022 Paul Bartlett