Libraries GuideChapter 11: Design Elements (X74_42 to X74_521)
X74_148
8- to 3-Line Cascadable Priority Encoder with Active-Low Inputs and Outputs
XC3000
| XC4000E
| XC4000X
| XC5200
| XC9000
| Spartan
| SpartanXL
| Spartan2
| Virtex
|
|---|
Macro
| Macro
| Macro
| Macro
| Macro
| Macro
| Macro
| N/A
| N/A
|
X74_148 8-input priority encoder accepts data from eight active-Low inputs (I7 - I0) and produces a binary representation on the three active-Low outputs (A2 - A0). The data inputs are weighted, so when more than one of the inputs is active, only the input with the highest priority is encoded, I7 having the highest priority. The active-Low group signal (GS) is Low whenever one of the data inputs is Low and the active-Low enable input (EI) is Low.
The active-Low enable input (EI) and active-Low enable output (EO) are used to cascade devices and retain priority control. The EO of the highest priority stage is connected to the EI of the next-highest priority stage. When EI is High, the data outputs and EO are High. When EI is Low, the encoder output represents the highest-priority Low data input, and the EO is High. When EI is Low and all the data inputs are High, the EO output is Low to enable the next-lower priority stage.
Inputs
| Outputs
|
|---|
EI
| I7
| I6
| I5
| I4
| I3
| I2
| I1
| I0
| A2
| A1
| A0
| GS
| EO
|
|---|
1
| X
| X
| X
| X
| X
| X
| X
| X
| 1
| 1
| 1
| 1
| 1
|
0
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 0
|
0
| 1
| 1
| 1
| 1
| 1
| 1
| 1
| 0
| 1
| 1
| 1
| 0
| 1
|
0
| 1
| 1
| 1
| 1
| 1
| 1
| 0
| X
| 1
| 1
| 0
| 0
| 1
|
0
| 1
| 1
| 1
| 1
| 1
| 0
| X
| X
| 1
| 0
| 1
| 0
| 1
|
0
| 1
| 1
| 1
| 1
| 0
| X
| X
| X
| 1
| 0
| 0
| 0
| 1
|
0
| 1
| 1
| 1
| 0
| X
| X
| X
| X
| 0
| 1
| 1
| 0
| 1
|
0
| 1
| 1
| 0
| X
| X
| X
| X
| X
| 0
| 1
| 0
| 0
| 1
|
0
| 1
| 0
| X
| X
| X
| X
| X
| X
| 0
| 0
| 1
| 0
| 1
|
0
| 0
| X
| X
| X
| X
| X
| X
| X
| 0
| 0
| 0
| 0
| 1
|
Figure 11.7 X74_148 Implementation XC3000, XC4000E, XC4000X, XC5200, XC9000, Spartan, SpartanXL