W78C354 Datasheet, PDF (36/44 Pages) Winbond – MONITOR MICROCONTROLLER

W78C354
If the bit VDISHC of SFR CONTREG2 is set high, the H-clamp pulse output will be disabled in the V
sync pulse period.
VDISHC
V_IN
HIN
H-clamp
Figure 16. Disable H-clamp output
M-6. Safe Operation Area (SOA) Output
The purpose of the SOA output is to protect the HOT (horizontal oscillating transistor) and other
critical circuitry by responding quickly if the Hsync frequency suddenly drops below a preset boundary
frequency. When the Hsync frequency is lower than the preset boundary frequency for three
consecutive cycles or stops for a certain period, the SOA pin (P1.5) will change to a "high" state to
activate an external circuit to protect the monitor. If the bit P15SF is set in SFR CONTREG4, the pin
P1.5 can be used as the SOA output (refer to Figure 17). The SOA pin can be released by writing any
value to SFR SOACLR.
CONDITION Of P15SF
PORT 1.5 I/O PIN FUNCTION
P15SF = 0
General I/O pin
P15SF = 1 & P1.5 = 0
SOA output
P15SF
P1.5 output latch
0
SOA output
1
P1.5/SOA
Figure 17. Alternate function of P1.5
• Boundary frequency HBOUN D = 2 MHz ÷ (Value of SOAREG)
Example: If 50 KHz is considered the boundary frequency, then value of SOAREG = 2M ¡Ò 50K =
40.
• No Hsync response time = 2048 × (1/FCLOCK).
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