7474 dual D flip-flop with preset and clear (74S74, 74LS74) pinout
DIP-14. Two positive-edge D flip-flops with preset and clear; dividers and synchronizers
On the Electron these make the PAL color timing. IC11 must be a 74S74: the service manual warns an LS part there makes the color circuit fail. Its two flip-flops, clocked on pins 3 and 11 by the 17.7345 MHz from the 74S04 pin 6, give 4.4336 MHz on pins 9 and 6 (pin 6 feeds the 74LS86 IC14 pin 1). IC12 is clocked from the ULA HS line; pin 5 shows about 7.7 kHz (the PAL line switch) and pin 9 must also be active. No color on UHF or composite with good RGB: these two, then the 74LS86s.
Open the interactive 7474 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | /1CLR | ctrl | Clear flip-flop 1 (Q low). |
| 2 | 1D | io | Data in, flip-flop 1. |
| 3 | 1CLK | clock | Clock 1, rising edge. |
| 4 | /1PRE | ctrl | Preset flip-flop 1 (Q high). |
| 5 | 1Q | io | Output Q, flip-flop 1. |
| 6 | /1Q | io | Inverted output, flip-flop 1. |
| 7 | GND | ground | Ground. |
| 8 | /2Q | io | Inverted output, flip-flop 2. |
| 9 | 2Q | io | Output Q, flip-flop 2. |
| 10 | /2PRE | ctrl | Preset flip-flop 2. |
| 11 | 2CLK | clock | Clock 2, rising edge. |
| 12 | 2D | io | Data in, flip-flop 2. |
| 13 | /2CLR | ctrl | Clear flip-flop 2. |
| 14 | VCC | power | +5 V. |
Fitted in
- Acorn Electron IC11 (74S74), IC12 (74LS74)