APPENDIX A: GPO Programming

Examples

The GPO control generation is based on the internal line

count and pixel count shown in

Figure 9 and Figure 10.Two

programmable registers (Vertical Start and Vertical Duration)

control the vertical component of the control signal. This

establishes at what line and for how many lines the control

signal will be active. Likewise, two programmable registers

(Horizontal Start and Horizontal Duration) control the hori-

zontal component of the control signal. The Horizontal reg-

ister values determine at what pixel count the signal goes

active and for how many pixel counts the signal stays active

during each line. The Vertical Component enables the signal

for however many lines programmed for and the Horizontal

Component generates pulses within that vertical time period.

Generally the following types of signals are generated:

1.

DC (either 1 or 0)

2.

A pulse every line

3.

A pulse once a frame (either in pixels or lines)

4.

Pulsed during active video (pulses are blanked during

vertical blanking period of frame)

Table 4 describes the programming requirements for general

types of pulses generated.

The GPO’s also have a “toggle mode”. This provides the

capability to generate a “REVERSAL” signal used in most

LCD applications. Bit 1 of the Control register is set toa1to

enable toggle mode operation. The GPO is programmed so

that a rising edge is produced when the control signal is

required to toggle. This generally occurs once each line.

Also, the # of edges generated per frame is programmed to

be an odd #. This ensures that the control signal will alter-

nate polarity from frame to frame.

Examples of GPO programming to produce specific control

signals are included in the following pages.

TABLE 4. GPO Pulse Generation

Vertical

Start

Vertical

Duration

Horizontal

Start

Horizontal

Duration

GPO Output

=don’t care

=0

=0

=0

Stuck 0 (When Output Polarity = 0)

Stuck 1 (When Output Polarity = 1)

Polarity control is in GPO Control Register bit 0

=don’t care

=0

#A

=0

Stuck 1 (When Output Polarity = 0)

Stuck 0 (When Output Polarity = 1)

Polarity control is in GPO Control Register bit 0

=don’t care

=0

#A

#B

(Note 29)

Pulse is generated every line beginning at

∼#A

32 MHz clocks from start of output line and lasting for

#B 32 MHz clocks

#A

#B

#C

=0

Pulse begins at line #A , clock #C and continues to

line #(A+B) pixel #C (multi-line pulse)

#A

#B

#C

#D

(Note 29)

Pulse generation begins at line A and continues for #B

lines. Each pulse begins at

∼pixel #C and lasts for D

counts

Note 29: Pulses will occur every other line if Horizontal Duration is greater than a line time.

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