P83CX80 Datasheet, PDF (60/84 Pages) NXP Semiconductors – 80C51 type core

Philips Semiconductors
Microcontrollers for monitors with DDC
interface, auto-sync detection and sync proc.
Product specification
P83Cx80; P87C380
19.2.5.3 Parameter Hpol
The mode change interrupt will be issued after 36 to 40
periods of the HSYNC when the polarity is changed from
negative to positive. The polarity indicator Hpol will be
changed from a logic 1 to a logic 0. The mode change
interrupt will be issued after the 60 periods of the HSYNC
when the polarity is changed from positive to negative. The
Hpol will be changed from a logic 0 to a logic 1. A logic 0
represents a positive polarity and a logic 1 represents a
negative polarity.
19.2.5.4 Parameter Hcha
If Hcha is set to HIGH indicating that the period time has
changed for a long period, the Hper and Hpres will be
updated. If the measured period time has become stable
then the two counters will start to count down and the
HENA signal is set to LOW again, thereby disabling the
register Hper and the SR flip-flop for Hpres parameter.
handbook, full pagewidth
HSYNC_P
Hres
FOSH
R
Q 11 to Q0
12-BIT
COUNTER
Hcnt
FOSH
D11 to D0
12-BIT
E _REGISTER
Q11 to Q0
HSYNC
DIV 16
Hper and Hpol
DECISION
CIRCUIT
S
Q
SR-FF
R
Q
D
Q
E D-FF
FOSH
HENA
Hlow
Hper
CHANGE
DETECTOR ^Hhgh
Hper
MODE
CHANGE
STABILIZATION
AND
COMPARISON
CIRCUIT
Hpres
FOSH
Hcha
MGG038
Hpol
Fig.29 Horizontal mode detection.
1997 Dec 12
60