PROGRAM COUNTER: 16 BIT REGISTER WHICH CONTAINS THE ADDRESS OF CONVERSION DECIMAL TABLE PROGRAM COUNTER ISSTEPPEDUPTOPOINTATTHE NEXT INSTRUCTION. PROM: PROGRAMMABLE READ ONLY MEMORY. THIS TYPE OF MEMORY THE INSTRUCTION BEING EXECUTED. DURING EXECUTION THE HEX 0 0 OCTAL 0 1 2 3 4 5 6 7 10 11 12 13 14 15 16 17 20 40 100 144 200 400 BINARY 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 ARRIVES BLANK. IT CAN BE PROGRAMMED BY THE USER WITH THE 1 2 3 4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 32 64 100 128 256 HELP OF A SPECIAL PROM BLOWER. ONCE THIS PROGRAM HAS BEEN PUT IN, IT CANNOT BE CHANGED. RAM: RANDOM ACCESS MEMORY. THIS IS THE STANDARD READ/WRITE MEMORY.
DATA (AND PROGRAMS) ARE LOST WHEN THE POWER IS SWITCHED OFF. REGISTER: STORAGE LOCATION IN THE MICROPROCESSOR ITSELF. THERE 5 6 7 8 9 A ARE INTERNAL REGISTERS A, X, Y, PC, S, P. • ROM: READ ONLY MEMORY. THIS IS MEMORY THAT HAS A PROGRAM PUT IN DURING PRODUCTION. THIS PROGRAM CANNOT EVER BE CHANGED, IT CAN ONLY BE READ. STORE: TRANSFERS DATA FROM AN INTERNAL REGISTER TO MEMORY. XTAL: THE CRYSTAL IN THE ACORN OSCILLIATES AT 1 MHZ. i.e. ONE B C D 1110 1111 10000 100000 1000000 1100100 10000000 100000000 THE ACORN MICROPROCESSOR IS DESIGNED TO DEAL WITH 8 BITS AT A TIME. THE COLLECTION OF 8 BITS IS GIVEN THE SPECIAL NAME 'BYTE', AND IS NORMALLY WRITTEN IN HEXADECIMAL OR BINARY.
A BYTE THUS IS 0....FF 16 ; 0....11111111 2 OR 0....255io. THE MICROPROCESSOR CAN CARRY OUT LOGICAL AND ARITHMETICAL MANIPULATIONS ON BYTES. 1.2 LOGICAL MANIPULATIONS THE MICROPROCESSOR CAN IMMEDIATELY CARRY OUT THE LOGICAL AND, E F 10 20 40 64 80 100 MILLION TIMES A SECOND. IT DOES THIS WITH GREAT ACCURACY. SO YOU CAN BUILD A CLOCK FROM YOUR ACORN. EXCLUSIVE - OR & OR FUNCTIONS ON ALL 8 BITS SIMULTANEOUSLY, USING THE FOLLOWING TRUTH TABLES FOR EACH BIT (SYMBOL V ) AND ( A ) EXCLUSIVE - OR ( V ) OR ( V ) bi 0 0 1 1 b 2 0 result 0 0 0 bi 0 0 1 1 b 2 0 result 0 bi 0 0 b 2 0 result 0 1 0 1 0 1 1 0 1 .
0 1 1 1 1 1 1 1 1 1 EXAMPLE OPERANDS 00111100 00111100 01011010 AND 01011010 (OPERATOR) 00011000 RESULT 01100110 00111100 01011010 OR E-OR 01111110