Commodore 128 Programmer's Reference Manual page 617

C128 HARDWARE SPECIFICATIONS 607
n
n
D0-D7
*TW is measured from the latest occurring of 02, CS, R/W
SYMBOL NAME
MIN TYP MAX
UNITS
Tw
Twh
Taws
Tah
TCh
Tvd
Tdh
Write Pulse Width
Write Hold Time
Address Set-up Time
Address Hold Time
Chip Select Hold Time
Valid Data
Data Hold Time
300 — —
0 — —
0 — —
10 — —
0 — —
80 — —
10 — —
ns
ns
ns
ns
ns
ns
ns
Figure 16-16. Write Cycle
EQUAL-TEMPERED
MUSICAL SCALE VALUES
The table in Chapter 11 lists the numerical values which must be stored in the SID
Oscillator frequency control registers to produce the notes of the equal-tempered musical
scale. The equal-tempered scale consists of an octave containing twelve semitones
(notes): C,D,E,F,G,A,B and C#,D#,F#,G#,A#. The frequency of each semitone is
exactly the 12th root of 2 (VY) times the frequency of the previous semitone. The table
is based on a <|>2 clock of 1.02 MHz. Refer to the equation given in the Register
Description in Chapter 11 for use of other master clock frequencies. The scale selected
is concert pitch, in which A-4 = 440 Hz. Transpositions of this scale and scales other
than the equal-tempered scale are also possible.
Although the table in Chapter 11 provides a simple and quick method for generat
ing the equal-tempered scale, it is very memory inefficient as it requires 192 bytes for
the table alone. Memory efficiency can be improved by determining the note value
algorithmically. Using the fact that each note in an octave is exactly half the
frequency of that note in the next octave, the note look-up table can be reduced from
ninety-six entries to twelve entries, as there are twelve notes per octave. If the twelve