74LS541 octal buffer (controller inputs) pinout
DIP-20. Buffers the controller port lines onto the data bus. U19 reads port 1, U18 reads port 2.
Two 3-state octal buffers put the controller lines on the data bus when a game reads $FC (port 1, U19) or $FF (port 2, U18). The strobes that pick joystick or keypad come from U24 (74LS00 latch), not from these chips. The Technical Manual's check: with nothing pressed, inputs (U18 pins 3-9, U19 pins 2-8) below 2.2 V mean a bad buffer. Its troubleshooting chart also names U24 and U6 for controller faults.
Open the interactive LS541 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | /G1 | ctrl | Output enable 1. On the ColecoVision both buffers take /IOE0R (I/O read $E0-$FF). |
| 2 | A1 | io | Input 1. U19: controller 1 pin 1 (up / keypad D0). |
| 3 | A2 | io | Input 2. U19: controller 1 pin 4 (right / keypad D1). |
| 4 | A3 | io | Input 3. U19: controller 1 pin 2 (down / keypad D2). |
| 5 | A4 | io | Input 4. U19: controller 1 pin 3 (left / keypad D3). |
| 6 | A5 | io | Input 5. U19: spinner A status from the spinner circuit (D4). UNVERIFIED |
| 7 | A6 | io | Input 6. U19: controller 1 pin 7 (spinner B, D5). |
| 8 | A7 | io | Input 7. U19: controller 1 pin 6 (fire, D6). |
| 9 | A8 | io | Input 8. U19: spinner interrupt status shared with U18 (D7). UNVERIFIED |
| 10 | GND | ground | Ground. |
| 11 | Y8 | data | Output 8 (3-state). U19 drives D7; U18 drives D0 (U18 runs the bus in reverse order). |
| 12 | Y7 | data | Output 7. U19: D6. U18: D1. |
| 13 | Y6 | data | Output 6. U19: D5. U18: D2. |
| 14 | Y5 | data | Output 5. U19: D4. U18: D3. |
| 15 | Y4 | data | Output 4. U19: D3. U18: D4. |
| 16 | Y3 | data | Output 3. U19: D2. U18: D5. |
| 17 | Y2 | data | Output 2. U19: D1. U18: D6. |
| 18 | Y1 | data | Output 1. U19: D0. U18: D7. |
| 19 | /G2 | ctrl | Output enable 2. U19 takes A1 directly (port 1 at $FC); U18 takes A1 through U7A (port 2 at $FF). |
| 20 | VCC | power | +5 V supply. |
Fitted in
- ColecoVision U18, U19