Acer SPECTRUM Series Service Manual page 49

2.3.2 Sync. Signal Support
The gmZAN2 chip supports digital separate sync (Hsync/Vsync), digital composite sync, and analog
composite sync (also known as sync-on-green). All sync types are supported without external sync
separation / extraction circuits.
Digital Composite Sync
The types of digital composite sync inputs supported are:
OR/AND type: No Csync pulses toggling during the vertical sync period
XOR type: Csync polarity changes during the vertical sync period
The gmZAN2 provides enough sync status information for the firmware to detect the digital composite sync
type.
Sync-On-Green (Analog Composite Sync)
The voltage level of the sync tip during the vertical sync period can be either –0.3V or 0V
2.3.3 Display Mode Support
A mode calculation utility (MODECALC.EXE) provided by Genesis Microchip may be run before
compilation of the firmware to determine which input modes can be supported. Refer to firmware
documents for more details.
2.4 Input Timing Measurement
As described in section 2.2.2 above, input data is sent from the analog-to-digital converter to the source
timing generator (STG) block. The STG block defines a capture window (Figure5).
The input timing measurement block consists of the source timing measurement (STM) block and interrupt
request (IRQ) controller. Input timing parameters are measured by the STM block and stored in registers.
Some input conditions will generate an IRQ to an external micro-controller. The IRQ generating conditions
are programmable.
2.4.1 Source Timing Measurement
When it receives the active CRT signal (R,G,B and Sync signals) the Source Timing Measurement unit
begins measuring the horizontal and vertical timing of the incoming signal using the sync signals and TCLKi
as a reference. Horizontal measurement occurs by measuring a minimum and a maximum value for each
parameter to account for TCLKi sampling granularity. The measured value is updated every line. Vertical
parameters are measured in terms of horizontal lines. The trailing edge of the Hsync input is used to check
the polarity of the Vsync input.
The table below lists all the parameters that may be read in the source timing measurement (STM)
registers of the gmZAN2.
Table 11. Input Timing Parameters Measured by the STM Block
Parameter
HSYNC Missing
VSYNC Missing
HSYNC/VSYNC Timing Change
HSYNC Polarity
VSYNC Polarity
Horizontal Period Min/Max
HSYNC High Period Min/Max
Vertical Period
VSYNC High Period
Horizontal Display Start
Horizontal Display End
Vertical Display Start
Vertical Display End
Interlaced Input Detect
CRC Data/Line Data
CSYNC Detect
Unit
N/A
N/A
N/A
Positive/Negative
Positive/Negative
TCLKs and SCLKs
TCLKs
Lines
Lines
SCLKs
SCLKs
Lines
Lines
N/A
N/A
N/A
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Updated at:
Every 4096 TCLKs and every 80ms (2-bits)
Every 80ms
When the horizontal period delta or the vertical
period delta to the previous line / frame
exceeds the threshold value (programmable).
After register read
Every frame
After register read
After register read
Every frame
Every frame
Every frame
Every frame
Every frame
Every frame
Every frame
Every frame
Every 80ms