| ??? 11/26/04 08:19 Modified: 11/26/04 08:21 Read: times |
#81993 - derivative depended Responding to: ???'s previous message |
hi,
I could imagine that some faster '52 derivatives have the strong pull-ups permanently activated. Then the direct connection of /WR and /RD line will result in destruction!
I would not proceed without an additional gate. Directly connecting both lines would cause some headaches... Absolutelly! And again: Nicolas uses external decoder IC and it is not a problem to change 138 decoder with 139 or 155 one. By the way: in some projects we do not use decoder in the whole. Instead decoder (139 or 155) + buffers/registers (245/574) we use multiplexors 251 as input selectors, and registers 259 as output buffers. They all have address lines and enable output/write inputs directly connected to /RD and /WR. Such configuration requires some program framework because uses bits` multiplexing/demultiplexing. From other side it eleminates decoder IC as well. Regards, Oleg |
| Topic | Author | Date |
| Regarding RD and RW pins | 01/01/70 00:00 | |
| Funeral Ceremony | 01/01/70 00:00 | |
| AND gate | 01/01/70 00:00 | |
| ...or roll your own AND gate | 01/01/70 00:00 | |
| Roll your own | 01/01/70 00:00 | |
| Why roll your own? | 01/01/70 00:00 | |
| why? | 01/01/70 00:00 | |
| the reason | 01/01/70 00:00 | |
| 74155 | 01/01/70 00:00 | |
| The micro may not burn | 01/01/70 00:00 | |
| Do Not Use The Diodes Scheme | 01/01/70 00:00 | |
| With Schottkys either... | 01/01/70 00:00 | |
No need | 01/01/70 00:00 | |
| Other use... and othe configuration | 01/01/70 00:00 | |
| Headaches or not... | 01/01/70 00:00 | |
| derivative depended | 01/01/70 00:00 | |
| Don't worry i used a gate.. | 01/01/70 00:00 |