The System Manual of SOL-20 - History of Computers

Sol THEORY OF OPERATION
PROCESSOR TECHNOLOGY CORPORATION
SECTION VIII
Figure 8-6. 6575 Character Generator ROM pattern.
For the second character position the Character and Line Address
Multiplexers call up the "T" in the Display RAM. The resulting
ASCII code for a "T" (1010100) ultimately appears on the address inputs
to the Character Generator ROM. Since the Scan Counter is still
at a count of zero, the ROM outputs 1111111. This process continues
for the balance of the displayable portion of the video scan line.
At the end of the horizontal scan line, the Scan Counter
changes to a binary count of 0001 which specifies scan line R1 in the
Character Generator ROM. The "C" and "T" are again called up from
the Display RAM for the first and second character position respectively.
The ROM consequently outputs 0100001 and then 0001000. This
sequence continues through scan line R8 when the Scan Counter is at a
count of 8 (1000) to produce the "C" and "T".
As discussed earlier, the Scan Counter cycles through 13
counts or scan lines. For the "C" and "T" in our example, the Scan
Counter has counted ten lines (15, 0, 1, 2, 3, 4, 5, 6, 7 and 8).
The remaining three scan lines are not used in forming the "C" or
"T", so on counts 9, 10 and 11 of the Scan Counter the Character
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