GS9021 datasheet(17/26 Pages) GENNUM

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5.3 Host Interface Read/Write Timing

Figure 9 illustrates valid times for reading/writing information

from the HOSTIF tables. Figure 9 represents two fields of

video data entering and exiting the GS9021. The relative

position of the EDH packet in the data stream is also shown.

(Note that the EDH packet entering the device at t0, EDH

F0, represents the EDH information from the previous field,

FIELD 0).

It is safe to read or write EDH information at least two lines

after an EDH packet exits the chip but before the

subsequent EDH packet enters the chip. Reading during

the time interval shown will show values from EDH F0.

Writing during the time interval shown will affect EDH F1.

Note that the above read/write timing should also be

observed when reading/writing flag information via the

FLAG PORT.

6.0 RESET

Setting the RESET input pin LOW re-initializes the internal

control circuitry including returning all HOST interface

programming values to their original default values. The

data pipe is not affected by the reset, so data continues to

flow through the chip unprocessed during resetting. An

internal power-on-reset cell is also present in the device so

that device initialization occurs on power-up. Figure 10a

illustrates the reset circuitry. The internal power-on reset

circuit of the GS9021 is sensitive to the rise time of the

power supply, hence an external power on reset chip or

board level reset line is strongly recommended.

When

using this technique, the user must ensure that a minimum

pulse width of 100ns is present on the reset line.

In applications where a board-level reset is not available, a

circuit similar to figure 10b can be used to ensure correct

reset on power-up. The RESET pin will typically take 1.4ms

to reach 2.5V on power up, but can take longer for power

supplies with slower rise times. A bleed resistor such as

the one shown (20k) will assist the capacitor to discharge

once power is removed. The user should allow the

capacitor to discharge to at least 0.5V before power is

reapplied, to permit a full internal reset. The time taken by

the RESET pin to reach 0.5V on power down, is dependent

upon the fall time of the power supply.

Fig. 1 Input Setup & Hold Times (Synchronous Inputs)

Fig. 2 Output Delay & Hold Times (Synchronous Outputs)

LOGIC OPR

HOST BIT

RESET

PCLKIN

SYNCHRONOUS

INPUTS

PCLKIN

DATA

VALID

SYNCHRONOUS

OUTPUTS

tOD

tOH

tOS

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