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4.0 S-LINK Usage Instructions

4.10 Link Down Function

A signal, LDOWN#, is provided on the LDC and LSC. If the LDC or LSC becomes aware of any problem which renders the S-LINK not functional, the LDC or LSC will set LDOWN# low and disable itself. If LDOWN# goes low during normal running, it is latched in that state even if the problem clears itself. LDOWN# can then only be removed by a reset cycle. This signal is asynchronous.

If either S-LINK card sets LDOWN# low, the other S-LINK card should set LDOWN# low, if this is possible.

LDOWN# is also set low during test mode. At the LSC, LDOWN# will go low when the LSC starts transmitting test patterns to the LDC. The time delay between UTEST# going low and LDOWN# going low is implementation dependent and is not specified. At the LDC, LDOWN# will go low at least one clock cycle of LCLK before the first test word is available. LDOWN# goes high again automatically when test mode is ended.

When a reset cycle is initiated at the LSC or LDC, LDOWN# goes low. When the reset cycle is complete, LDOWN# goes high automatically.

Notice that the only circumstance in which data can be transferred out of the LDC (LWEN# low, LCLK running) when LDOWN# is low is when the S-LINK is in test mode.

LDOWN# will also be low immediately on power-up, while the S-LINK card is completing its power-up configuration. When the power-up configuration is complete, LDOWN# will go high automatically.

The designer of the motherboard shall ensure that if the LSC or LDC is not powered-up or is not present, the motherboard will pull LDOWN# low.

The S-LINK Interface Specification - 27 MARCH 1997
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