Toshiba TMP91C815F Data Book page 221

Settlement of Frame frequency function
3.14.4.1
TMP91C815 defines so-called frame period (refresh interval for LCD panel) by the value set in fFP[8:0] .
DLEBCD pin outputs pulse every frame period. DLEBFR pin usually outputs the signal inverts polarity every
frame period.
Basic Frame period ; DLEBCD signal , is made according to the resister fFP[8:0] setting mentioned before.
However this fFP[8:0] setting is generally equal to common number , frame period can be corrected by
increasing fFP[8:0] with ease.
The equation can calculate frame period .
Frame period = LCDCK / ( D x fFP) [Hz]
Please select the value of fFP[8:0] as the frame period you want to set in thetable 3.14.4.
(Note) : Please make the value set to fFP[8:0] into the following range.
COM(common number) ≦ FR ≦ 320
(EX.1) : In the case where frame period is set to 72.10Hz by 240coms.
Therefore, LCDCTL<FP8> = 1 and LCDFFP<FP7: 0> = 2FH are set up.
fFP =240(COM)+63 = 303 = 12FH ( by table 3.14.4 )
91C815-
D: constant for each common(table 3.14.4)
FFP: setting of fFP[8:0] resister
LCDCK: source clock of LCD
( low clock is usually selected )
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TMP91C815