Level-sensitive scan design
(circuit design) (LSSD) A kind of
scan design which uses separate system and scan clocks to distinguish between normal and test mode.
Latches are used in pairs, each has a normal data input, data output and clock for system operation.
For test operation, the two latches form a master/slave pair with one scan input, one scan output and non-overlapping scan clocks A and B which are held low during system operation but cause the scan data to be latched when pulsed high during scan.
____ |
| Sin ----|S
| A ------|>
| |
Q|---+--------------- Q1 D1 -----|D
|
| CLK1 ---|>
|
| |____|
|
____ |
|
| +---|S
| B -------------------|>
| |
Q|------ Q2 / SOut D2 ------------------|D
| CLK2 ----------------|>
| |____|
In a single latch LSSD configuration, the second latch is used only for scan operation.
Allowing it to be use as a second system latch reduces the silicon overhead.
