tmp88cs38ng TOSHIBA Semiconductor CORPORATION, tmp88cs38ng Datasheet - Page 186

• Manufacturer Part Number: tmp88cs38ng
• Description: Cmos 8-bit Microcontroller
• Manufacturer: TOSHIBA Semiconductor CORPORATION

2.15.5.8.1 Operating Principle
a comparator and an oscillator controller. The frequency of the ring oscillator
depends on the cycle of the external
oscillator generates clocks required for one scanning line and the 11-bit counter
counts the number of clocks. Then the counted number of the upper-order 8 bits is
compared with the value set by ORCLCK. The comparator sends the compared
result, which controls the ring oscillator and changes the oscillating frequency. At
the frequencies of 8 MHz, 16 MHz and 24 MHz set by ORCLKC, the error
percentages are 1.65%, 0.83% and 0.55% respectively. Thus, even when the same
value is rewritten to ORCLKC, the display position after refresh deviates by the
error percentage (Note 1).
from the comparator. To avoid display jitter created by fine adjustment, the oscillator
controller receives a coincidence signal and automatically stops adjusting the ring
oscillator. After the ring oscillator becomes stable, it drives a display clock at a
regular frequency. The output frequency fluctuates according to changes of
temperature and voltage (Note 2). The frequency of the ring oscillator can be
adjusted to the required frequency (Display position) by writing value to ORCLKC in
response to the change of condition.
control, please writes value before adjustment to ORCLKC.The comparator
compares ORCLKF (the result from comparing the counted number of the
upper-order 8 bits of the 11-bit counter with the ORCLKC setting value.) with the
ORCLKC setting value.
checked and please writes values before adjustment to ORCLKC.
Therefore, care must be taken to the interval of adjusting the frequency of the ring
oscillator.
Note 1: Since the clock generator for OSD display controls the frequency using the
The clock generator for OSD display consists of a ring oscillator, an 11-bit counter,
The oscillator controller controls the operation of the ring oscillator using a result
When the oscillating frequency of the ring oscillator is adjusted under software
Comparing ORCLKF with ORCLKC, the deviation of the oscillating frequency is
In this case, the deviation of the display position occurs as described in Note 1.
upper-order 8 bits of the 11-bit counter, the low-order 3 bits do not participate in
determining the frequency. This yields an error equal to relative magnitude of the
low-order 3 bits at maximum. Even when the same value is set to a register, up to
8-count error occurs in one line. (Errors when using clock generator for OSD
display in NTSC (interlace) mode (HD = 53.2 μs) are explained subsequently.)
88CS38-186
HD
input and the ORCLKC setting. The ring
TMP88CS38/CM38A/CP38A
2007-09-12