Datasheet

AD9979
Rev. C | Page 27 of 56
GENERAL-PURPOSE OUTPUTS (GPO)
The AD9979 provides programmable outputs to control a
mechanical shutter, strobe/flash, the CCD bias select signal,
or any other external component with general-purpose (GP)
signals. Two GP signals are available, with up to two toggles
each, that can be programmed and assigned to GPO1 and
GPO2. These pins are bidirectional and also allow visibility of
CLPOB, PBLK, and internal high speed signals (as an output)
and external control of HBLK (as an input). The registers
introduced in this section are described in Table 16.
Primary Field Counter
The AD9979 contains a primary field counter that is used to
count multiple fields when using the GPO output signals. This
counter is incremented on each VD cycle. The primary counter
has several modes of operation controlled by Address 0x50,
including the following:
• Activate counter (single count)
• RapidShot (repeating count)
• ShotTimer (delayed count)
• Force to idle
The primary counter regulates the placement of the GP toggle
positions. In addition, if the RapidShot feature is used with the
primary counter, the counter automatically repeats as necessary
for multiple expose/read cycles.
GP Toggles
When configured as an output, each GPO can deliver a signal
that is the result of programmable toggle positions. The GP
signals are independent and can be linked to a specific VD
period or over a range of VD periods, via the primary field
counter, through the GP protocol register (Address 0x52). As
a result of their associations with the field counters, the GP
toggles inherit the characteristics of the field counter, such as
RapidShot and ShotDelay. To use the GP toggles
1. Program the toggle positions (Address 0x54 to
Address 0x59)
2. Program the protocol (Address 0x52)
3. Program the counter parameters (Address 0x51)
4. Activate the counter (Address 0x50)
For Protocol 1 (no counter association), skip Step 3 and Step 4.
With these four steps, the GP signals can be programmed to
accomplish many common tasks. Careful protocol selection and
application of the primary counter yields efficient results to
allow the GP signals smooth integration with system operation.
Several simple examples of GPO application using only one GPO
and one field counter follow. These examples can be used as
building blocks for more complex GPO activity. In addition,
specific GPO signals can be passed through a four-input LUT to
realize combinational logic between them. For example, GPO1
and GPO2 can be sent through an XOR look-up table, and the
result can be delivered on GPO1, GPO2, or both. In addition,
either GPO1 or GPO2 can deliver its original toggles.
Table 15. Primary Field Counter Registers (Address 0x50 and Address 0x51)
Name Length Description
PRIMARY_ACTION 3 bits 0x0 = idle (no counter action). GPO signals still can be controlled using polarity or GPx_PROTOCOL = 1.
0x1 = activate counter. Single cycle of counter from 1 to counter maximum value; then returns to idle state.
0x2 = RapidShot. After reaching maximum counter value, counter wraps and repeats until reset.
0x3 = ShotTimer. Active single cycle of counter after added delay of N fields (use PRIMARY_DELAY register).
0x4 = test mode only.
0x5 = test mode only.
0x6 = test mode only.
0x7 = force to idle.
PRIMARY_MAX 4 bits Primary counter maximum value.
PRIMARY_DELAY 4 bits ShotTimer. Number of fields to delay before the next primary count starts.