mc68hc05bs8 Freescale Semiconductor, Inc, mc68hc05bs8 Datasheet - Page 82

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

9
9.8
The CPU will process an Sync Signal Processor VSYNC interrupt if the following conditions are
satisfied:
This interrupt will vector to the interrupt service routine located at the address specified by the
contents of $3FF8 and $3FF9. The VSYNC interrupt latch will be cleared automatically by fetching
of these vectors.
This allows an interrupt to be generated in each vertical frame after a certain number of lines
(0-127) to check the status of the monitor and conditions.
9-6
1) the I-bit of the CCR is cleared,
2) the VSIE bit of the Interrupt Line Count register (ILCR) is set, and
3) the value of the horizontal line counter matches the value set in the ILCR.
Counter signal reset
VSYNC Interrupt
PO2 64
case 1
PO2 64
case 2
1. The value of the counter will be loaded into the register before it is reset.
2. The Vertical Frequency Counter is clocked by a PO2 64 clock.
3. Because of the asynchronous nature between PO2 and VSYNIN, the register
VSYNC
will have one more count in case 2 than in case 1.
PO2
Figure 9-4 Vertical Frequency Counter Timing
Counter resets at 16 PO2 cycles
after falling edge of VSYNIN
SYNC SIGNAL PROCESSOR
Counter advances at the
rising edge of the clock
MC68HC05BS8
TPG