Digit Clock

Shows a 24-hour clock in large digits on a yellow screen. Each digit is drawn by enlarging the ROM character set, with a round UDG dot standing in for every lit pixel. You enter the starting time as HHMM, and the display then advances one minute at a time while a small counter ticks off the seconds below it. Every quarter hour it plays a chime, one phrase at quarter past, two at half past, three at quarter to and four on the hour, and it changes the border to a random color.

Program Analysis

Program Structure

Lines 20–30 define UDG a as a filled circle. Line 1030 converts the HHMM input into minutes since midnight in M. Lines 1045–1120 split M into four digits and draw them at columns 0, 7, 16 and 23, with a colon made of two dots at column 15. The minute loop at 1130–1140 counts 0 to 54 with PAUSE 57 per step, followed by PAUSE 21. This is timed so that the counting, the pauses and the redraw add up to about a minute. M wraps at 1440.

Big Digits

The subroutine at 1500 reads the digit’s bitmap straight from the ROM character set, starting at 15745 (the “0” pattern at 15744, skipping its blank top row). For six rows it tests the top bit of each byte, prints CHR$ 144 (the dot) or a space, and doubles the byte to shift the next bit up, for seven columns. The result is a 7×6 block of characters. OVER 1: PRINT TAB T; moves to the next row without wiping the digit next to it, because spaces printed with OVER 1 leave the screen unchanged.

Chimes

When M is a multiple of 15, the subroutine at 2000 plays four-note phrases (pitches 12, 8, 10, 3 and 3, 10, 12, 8), which follow the Westminster quarter pattern. It stops after the number of phrases matching the minutes value in S, then sets BORDER RND*7.

Potential Issues

• Timing depends on PAUSE and BASIC execution speed, so the clock will drift. The seconds counter shows 0–54, not 0–59.
• The time input is not checked, so minutes of 60 or more are accepted.
• The tape header has no autostart line, so the program has to be started with RUN after loading, even though line 10 suggests it was meant to be saved with LINE 1.