Avago Technologies LSI53C140 - Manual (Page 32)

2-14 Functional Descriptions
Ver. 2.1 Copyright © 1998–2001 by LSI Logic Corporation. All rights reserved.
2.2.11.2 Warm Swap Enable (WS_ENABLE/)
This input removes the chip from an active bus without disturbing the
current SCSI transaction (for Warm Swap). When the WS_ENABLE/ pin
is asserted, after detection of the next bus free state, the SCSI signals
are 3-stated. This occurs so that the LSI53C140 no longer passes
through signals until the WS_ENABLE/ pin is deasserted HIGH and both
SCSI buses enter the Bus Free state. As an indication that the chip is
idle, or ready to be warm swapped, the XFER_ACTIVE signal deasserts
LOW. An LED or some other indicator could be connected to the
XFER_ACTIVE signal. This feature of Warm Swap Enable is to isolate
buses in certain situations.
Table 2.6 describes the WS_ENABLE/ signal
polarity.
2.2.11.3 Transfer Active (XFER_ACTIVE)
This output is an indication that the chip has finished its internal testing,
the SCSI bus has entered a Bus Free state, and SCSI traffic can now
pass from one bus to the other. The signal is asserted HIGH when the
chip is active.
Table 2.7 describes the XFER_ACTIVE signal polarity.
Table 2.6 WS_ENABLE/ Signal Polarity
Signal Level State Effect
LOW = 0 Asserted Requests the LSI53C140 to go off-line after
detection of a SCSI Bus Free state.
HIGH = 1 Deasserted Enables the LSI53C140 to run normally.
Table 2.7 XFER_ACTIVE Signal Polarity
Signal Level State Effect
HIGH = 1 Asserted Indicates normal operation, and enables
transfers through the LSI53C140.
LOW = 0 Deasserted Detects a Bus Free state by the LSI53C140
due to WS_ENABLE/ being low, thus disabling
transfers through the device.