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Abstract
THE COSMAC EK/Assembler-Edtior kit CDP 18S024 of RCA is based upon CMOS microprocessor CDP 1802 and operates on + 10V supply. The kit includes 4 kbytes of RAM and utility program UT4 of 512 bytes. For addition of extra memory, address decoders are necessary. A decoder card has been designed to provide full 64 kbyte memory expansion. Erasable and reprogrammable read-only memory EPROM are convenient media for storage of programs. However, popular EPROM type2708 operates on +5V, +12Vand–5 volts and its input and output are TTL compatible. Level shifters and tristate buffers have therefore been included in the same printed circuit board to enable data transfer from EPROM output lines to CDP 1802, bidirectional databus.
Last 16 kbyte and 1 kbyte at address 8000 have been reserved for EPROM usage. Assembler, Editor and BASIC were written on EPROM. Utility program UT4 has been modified to call these programs by $A, $E and $B respectively. Modified utility program has been written on EPROM and it replaces the existing utility program of the kit. It is similar to latter in all respects except for the extra facilities.