S39421 View Datasheet(PDF) - Summit Microelectronics
Part Name
Description
MFG CO.
'S39421' PDF : 28 Pages View PDF
S39421
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.
In Figure 13, DD is tied to VCC through a pull-up resistor.
This will allow only a single download after power on. The
actual download function would not be enabled until
tPURST had expired and CS was brought high. As soon as
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.
System
Reset
RESET
DD
2024 ILL8.0
FIGURE 12. DD DISABLED
System
Reset
RESET
DD
2024 ILL9.0
FIGURE 13. ONE TIME DOWNLOAD
RESET
I/Oe
ASIC I/Oa
I/Ob
I/Oc
I/Od
RESET
DD
SK
DO
DI
CS
FIGURE 14. ASIC CONTROL
2024 ILL10.0
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.
2024 9.0 8/8/00
14
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