ST92185B STMicroelectronics, ST92185B Datasheet - Page 137

• Manufacturer Part Number: ST92185B
• Description: 16k/24k/32k Rom Hcmos Mcu With On-screen-display
• Manufacturer: STMicroelectronics

SYNC CONTROLLER (Cont’d)
7.5.1 H/V Polarity Control
Two control bits manage the H/V polarities. HPOL
(SCCS0R.6) manages the HSYNC polarity (a pos-
itive polarity assumes the leading edge is the ris-
ing one). VPOL (SCCS0R.7) controls the VSYNC
polarity.
7.5.2 Field Detection
Field detection is necessary information for the
Display controller for fringe and rounding features.
To determine correctly the field in case of using
separate H and V input signals, it is necessary to
provide an internal compensation of the hardware
delay generated on VSYNC (VSYNC is generally
issued by integrating the equalization pulses).
Therefore the VSYNC leading edge is compared
to the leading edge of an internally delayed
HSYNC.
The delay applied to HSYNC is software program-
mable through the SCCS0R (3:0) bits (from 0 to 63
µs). It must be calculated by the user as being the
time constant (modulo 64 µs) used to extract
VSYNC by the other components of the chassis.
7.5.3 Interrupt Generation
The SYNC Controller unit can provide two different
interrupts to the ST9+ Core. The first interrupt ap-
pears at each beginning of field upon detection of
the Vertical Sync pulse coming from the deflection
circuitry (i.e. from VSYNC); it is called the “Field
start” interrupt. A flag is associated to this inter-
rupt, called “FLDST” (SCCS1R.6). This flag is set
to “1” by hardware when the Vertical Sync pulse
appears. It must be cleared by software.
The second interrupt appears at the end of each
Vertical Blank Interval. It is generated at the begin-
ning of the line 25 counted from the deflection cir-
cuitry (i.e. from VSYNC); and is called the “End OF
VBI” interrupt. A flag is associated to this interrupt,
called “EOFVBI” (SCCS1R.7). This flag is set to
“1” by hardware when the line 25 starts. It must be
cleared by software.
These two interrupts EOFVBI and FLDST are re-
spectively attached to the INT4 and INT5 external
interrupt inputs of the ST9+ Core. The leading
edges of the 2 interrupt requests are the falling
ones. (For more details, refer to the Interrupts
chapter).
7.5.4 Sync Controller Working Modes
Different working modes are available fully control-
led by software.
The first two working modes assume that TV de-
flection sync signals are available and stable.
The last two modes assume that no TV signal is
available. The chip works in a free-running mode
providing standard TV Sync signals based on the
main internal 4 MHz clock.
Switching from one mode to any other is done un-
der full software control, through the programming
of two control bits called as MOD1 and MOD0.
These control bits are described in the SCCS1R
register
7.5.4.1 Standard Sync Input Mode
This mode is accessed when both MOD1 and
MOD0 bits are reset.
In this mode, the µP receives the chassis synchro
through two separate inputs. These are VSYNC
and
(SCCS0R.5) is reset.
HSYNC.
ST92185B - SYNC CONTROLLER
It
also
assumes the
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VSEP