4.0 S-LINK Usage Instructions
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.