74LS138 3-to-8 decoder pinout
DIP-16. 3-to-8 line address decoder.
A 3-to-8 line decoder with three enables. On HERO 1 the four copies pick the 8K memory blocks and the $C200-$C300 I/O ports from the upper address lines. A stuck output means one block is always selected or never selected, so the ROM or RAM there will not answer.
Open the interactive LS138 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | A | addr | Select input A (lowest address bit of the group). |
| 2 | B | addr | Select input B. |
| 3 | C | addr | Select input C. |
| 4 | /G2A | ctrl | Enable 2A, active low. |
| 5 | /G2B | ctrl | Enable 2B, active low. |
| 6 | G1 | ctrl | Enable 1, active high. |
| 7 | /Y7 | ctrl | Output 7, active low. |
| 8 | GND | ground | Ground. |
| 9 | /Y6 | ctrl | Output 6, active low. |
| 10 | /Y5 | ctrl | Output 5, active low. |
| 11 | /Y4 | ctrl | Output 4, active low. |
| 12 | /Y3 | ctrl | Output 3, active low. |
| 13 | /Y2 | ctrl | Output 2, active low. |
| 14 | /Y1 | ctrl | Output 1, active low. |
| 15 | /Y0 | ctrl | Output 0, active low. |
| 16 | VCC | power | +5 V supply. |
Fitted in
- HERO 1 U403, U406, U421, U422
- ColecoVision U5, U6
- BBC Micro Model B IC24