| ??? 04/14/08 22:04 Read: times |
#153308 - More Port 0 history Responding to: ???'s previous message |
In the early days of MOS, transistors operating off of 5 volts were quite weak. They were barely able to drive 1 TTL load (1.6 mA). In addition, the pullup value was not well controlled. It might vary over a 4:1 range.
There were two things that could go wrong with a pullup. First, in the case of strong pullups, the chip might fail to meet the TTL low level spec, causing chip failure. It might also slow down the data bus, and thereby affect the maximum processor speed. It was considered a better solution to let the customer add their own pullups to the data bus. When in doubt, throw it out. |
| Topic | Author | Date |
| P0 pull up resistors | 01/01/70 00:00 | |
| ports structure | 01/01/70 00:00 | |
| More Port 0 history | 01/01/70 00:00 | |
| Of course, there is a reason for it... | 01/01/70 00:00 | |
| Port 0 Pullups WHY??? | 01/01/70 00:00 | |
| P0 is multiplexed for input/output; P2 is not | 01/01/70 00:00 | |
| This would all be perfectly obvious if only you\'d | 01/01/70 00:00 | |
| See this thread | 01/01/70 00:00 | |
| Scary Bible | 01/01/70 00:00 | |
| Only In Some Cases.... | 01/01/70 00:00 | |
| Directly connecting the base will hardly work! | 01/01/70 00:00 | |
| Hardly is correct.... | 01/01/70 00:00 | |
| what about a darlington? | 01/01/70 00:00 | |
| Will also turn off the weak pull-up... | 01/01/70 00:00 | |
| The high state is adequate for some things | 01/01/70 00:00 | |
OH | 01/01/70 00:00 |