mc68hc05bs8 Freescale Semiconductor, Inc, mc68hc05bs8 Datasheet - Page 78

• Manufacturer Part Number: mc68hc05bs8
• Description: Mc68hc05 Family Of Low-cost Single-chip Microcontrollers.
• Manufacturer: Freescale Semiconductor, Inc

9
9.2
The polarity correction block of the sync signal processor accepts the input sync signals and
converts them to negative polarity signals, regardless of the polarity of the inputs. The following
describes the methodologies used in polarity correction.
9.2.1
To test the polarity of the input sync signal, the duration of the low pulse is examined. If the low
period is longer than a specific value (512 s or 1024t
sync, the input sync will be inverted before output. For negative polarity input sync signal, it is
anticipated that the duration of the low pulse would be shorter than the specific value, and the input
sync signal passes through to the output without inversion.
This polarity correction is a continuous process, and the error margin is equal to the maximum
permissible sync pulse width specified (512 s or 1024t
negative polarity at input is assumed.
9.2.2
Since the input at HSYNC can be either a pure horizontal sync signal or a composite sync signal,
different methodologies are used in polarity correction.
Unlike the polarity correction for VSYNC, both the high pulse and low pulse of the sync signal at
HSYNC are examined. If the pulse, either active high or low, is longer than a certain period (8 s
or 16 t
sync signal will be confirmed as a positive polarity sync signal, and will be inverted. If there are 8
consecutive high long pulses, it will be confirmed as a negative polarity sync signal.
The operation of this module is also continuous, and the error margin is equal to the period of the
pre-set number (default is 8) of horizontal sync pulses. At power-up or system reset, negative
polarity at input is assumed.
9-2
CYC
), it will be regarded as a long pulse. If there are 8 consecutive low long pulses, the input
Polarity Correction
Separate Vertical Sync Input
Separate Horizontal or Composite Sync Input
SYNC SIGNAL PROCESSOR
CYC
), as in the case of positive polarity input
CYC
). At power-up or system reset,
MC68HC05BS8
TPG