Appeal 2007-2127
Reexamination Control No. 90/006,621
can only input the characters from the keyboard as fast as they are to
be sent. On the other hand, in the interrupt mode, the microcomputer
continues to send code and you can type ahead. The interrupt routine
takes so little time that fetching a character and storing it in the buffer
cannot be discerned in listening to the Morse code character string.
9. The interrupt is a clock-activated interrupt, but a keyboard-activated
interrupt is also disclosed (page 278):
Ideally one would use the keyboard strobe itself to produce one
interrupt whenever a key was pressed. Because this strobe is not very
accessible, we have chosen to use the 6522 T1 timer in its free-
running mode to generate IRQ¯¯¯ -type interrupts every 65,537 clock
cycles. . . . For most people the 65,537 clock cycles between
interrupts will produce a rapid enough interrupt rate.
10. The 6522 T1 timer produce continuous interrupts by repeatedly
counting down the number stored in the T1 interval timer at the system clock
rate of 1.023 MHz (pages 235-244), so 65,537 clock cycles takes about
0.064 seconds or 64 milliseconds.
11. In normal operation the Morse code translation main program is
continuously executed by the CPU, taking characters from the buffer and
outputting them as Morse code (Figure 10-3, page 279).
12. A clock periodically interrupts the main program frequently enough to
appear that the interrupt routine and the Morse code program are operating
simultaneously (page 278).
13. The interrupt service routine saves the registers ("Save the Registers"
block, Figure 10-2, page 277) and checks for a new input character from the
keyboard ("Key Pressed?" decision block, Figure 10-2).
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