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AD9927

Rev. 0 | Page 63 of 100

GP LOOK-UP TABLES (LUT)

The AD9927 is equipped with a look-up table for each pair of

consecutive GP signals when configured as outputs. GP1 is

always combined with GP2, GP3 is always combined with GP4,

GP5 is always combined with GP6, and GP7 is always combined

with GP8. The external GPO outputs from each pair can output

the result of the LUT or the original GP internal signal.

GP1

LUT

GPO2

GPO1

GP2

GP2_USE_LUT

GP1_USE_LUT

Figure 76. Internal LUT for GP1 and GP2 Signals

Address 0x79 dictates the behavior of the LUT and which

signals receive the result. Each 4-bit LUT_FOR_GPxy register

can realize any logic combination of GPx and GPy. For example,

Table 43 shows how the register values of LUT_FOR_GP12 [11:8]

are determined. XOR, NAND, AND, and OR results are shown,

but any 4-bit combination is possible. A simple example of XOR

gating is shown in Figure 77.

Table 43. LUT Results Based on GP1, GP2 Values

GP2

GP1

LUT: XOR

LUT: NAND

LUT: AND

LUT: OR

GP1

GP2

GPO2

NOTES

1. LOGIC COMBINATION (XOR) OF PROGRAMMED TOGGLES

GP1 AND GP2.

LUT_FOR_GP12[11:8] = 0x06

GP2_USE_LUT = 1

GP1_USE_LUT = 0

GPO1

Figure 77. LUT Example for GP1 XOR GP2

Field Counter and GPO Limitations

The following is a summary of the known limitations of the

field counters and GPO signals that dictate usability.

• The field counter trigger (PRIMARY_ACTION and

SECONDARY_ACTION registers, Address 0x70) is self-reset

at the start of every VD period. Therefore, there must be one

VD period between sequential programming to that address.

• If GP*_PROTOCOL = 1, it must be manually reset to

GP*_PROTOCOL = 0 one VD period before it can be

used again. If manual toggles are desired in sequential fields,

the MANUAL_TRIG register should be used in conjunction

with GP*_PROTOCOL = 1.

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