2. Physics 413 Chapter 5

3. Well-Connected Monitor is TV screen attached to your PC Monitor is software “burned” (stored) in ROM. It boots up your computer. Incidentally, on the IBM PC, the monitor ROM is better known as BIOS ROM.

4. OUTCH LDAA # $ 37 JSR $$ FE3A LDAA # $ 06 JSR $$ FE3A Program displays “ HI ”. The built-in subroutine is called OUTCH (output character) and is stored in ROM at the address FE3A

5. Secret Codes!

6. OUTCH is a Pain! JSR FE52 37 4F 0E FE Program displays HELLO and uses the subroutine OUTSTR located at FE52 and works better for displaying character strings. The last character must include the decimal point.

7. Interrupts InterruptHeathkit Redirected Vectors IRQ00F7 SWI00F4 NMI00FD RESETFC00 The programmer who writes the ISR for IRQ (and that's you!) must simply put a jump instruction at 00F7. Something like JMP 0050. At 0050 there will be plenty of room to write an ISR

8. The Mask! SEISet interrupt maskDisable IRQ CLIClear interrupt MaskEnable IRQ Incidentally, the interrupt mask is a flag in the CCR. The software instructions, SEI and CLI simply set and reset this flag.

9. 6800 Pinout Diagram

10. Address Decoder

11. A Flashy Decoder

12. Data Output Circuit