74LS125 quad 3-state buffer pinout
DIP-14. Drive-side 3-state gates: write protect, read data, write data, write request
Four non-inverting buffers, each with its own active-LOW enable. On the Disk II analog card two of them put W PROT and RD DATA on the shared ribbon only while this drive is enabled; the other two gate WR DATA and write request. It sits on the +5 V rail, so it dies with C4 when +12 V reaches the 5 V pins (misplugged ribbon, or a card plugged in with power on).
Open the interactive 74LS125 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | /1G | ctrl | Enable for gate 1 (write protect): LOW while the drive is enabled. |
| 2 | 1A | io | Write-protect switch input (R12 10 kΩ pull-up; the switch returns to phase 1). |
| 3 | 1Y | io | W PROT to ribbon pin 20. |
| 4 | /2G | ctrl | Enable for gate 2 (write data), from the write-request logic. |
| 5 | 2A | io | WR DATA from ribbon pin 18. |
| 6 | 2Y | io | Write data to the CA3146 head driver. |
| 7 | GND | ground | 0 V. |
| 8 | 3Y | ctrl | Buffered write request (R16 1 kΩ pull-up) to ULN2003 pin 7 and the 2G enable. |
| 9 | 3A | ctrl | /WR REQ from ribbon pin 10 (R15 1 kΩ pull-up). |
| 10 | /3G | ctrl | Enable for gate 3 (write request). |
| 11 | 4Y | io | RD DATA to ribbon pin 16 (R13 15 kΩ pull-up on rev H); TP1. |
| 12 | 4A | io | Read pulse from the MC3470 output stage. |
| 13 | /4G | ctrl | Enable for gate 4 (read data): LOW while the drive is enabled. |
| 14 | VCC | power | +5 V. |
Fitted in
- Disk II B4 on the analog card (socketed, Apple 305-0125)
- DuoDisk B3 (cards 676-11101/11102) or C3 (676-11107) on the analog card