4 ms·
How did the firmware modify the data in the shift register to write text? Did it require cycle-accurate delay loops to hit it at just the right cycle?
by tlb 5y ago
How did the firmware modify the data in the shift register to write text? Did it require cycle-accurate delay loops to hit it at just the right cycle?
- kens 5y agoIt's pretty clever. One shift register held a bit to indicate the current cursor position. To write a character, the circuit waited until the cursor bit appeared and then updated the character shift registers. At the same time, the cursor bit was delayed to advance it to the next character. Note that you could only write characters sequentially; you couldn't write to arbitrary locations on the screen.