14

S39421

2024 9.0 8/8/00

Data Download Control

There are a number of ways to implement the data

download mode of operation. For applications that do not

require use of this feature, simply ground the DD pin and

disable the function altogether.

RESET

DD

System

Reset

2024 ILL8.0

FIGURE 12. DD DISABLED

FIGURE 14. ASIC CONTROL

FIGURE 13. ONE TIME DOWNLOAD

RESET

DD

CS

SK

DO

DI

ASIC I/Oa

I/Ob

I/Oc

I/Od

I/Oe

RESET

2024 ILL10.0

This will allow only a single download after power on. The

actual download function would not be enabled until

CS is deselected the DD mode will be disabled. The

primary disadvantage to this method is the lack of a reload

after brownout. The DD mode may or may not be initiated

depending on how low the power is cycled.

In Figure 14, the S39421 DD mode is 100% under the control of the add-in board’s ASIC. The pull-down resistors insure

CS and DD do not float while the ASIC is in a reset state or shortly thereafter, which may lead to spurious activity on

CS and DD, possibly indicating a false DD request.

System

Reset

RESET

DD

2024 ILL9.0