| ??? 11/03/05 15:53 Modified: 11/03/05 16:01 Read: times |
#103270 - Trace lengths and buffering. Responding to: ???'s previous message |
Dear Erik,
Thanks for your prompt reply with helpful answer. Erik said:
Anyhow, if you keep the XTAL and associated capacitor traces extremely short, you shoud not have a problem with this. I return PCB layouts to the laoyout person if such traces exceed 0,5". I do keep XTAL and burden caps trace lengths very short never exceeding 7 to 8 mm. Erik said:
However you may have a problem since it is usually a very bad idea to let unbuffered port pins leave the board. You are right erik. The 21 pins I am routing to connector are for a 6 digit seven segment display and a 6 key linear keypad. The 8 segments drives [ including decimal ] will be buffered using 74LS541 and 6 digit drives will be using BC557 transistors. I was planning to use 6 keypad signals unbuffered. is it ok to leave them unbuffered or it is better to put a buffer such as 74HC541. Erik said:
You do not state how long the ribbon cable is and what is on "the other board" so, no absolutes here. The ribbon cable is standard FRC ribbon cable simillar to that used in ATA harddisks. The length will be 3 to 4 inches. This ribbon cable doesnt leave the box. I tried to search and found this post by Mike posted an year back in reply to my board design discussed the issue of Encircling crystal with signals. [ Please see last para. ] http://www.8052.com/forum/read.phtml?id=74388 Thanks & Regards, Prahlad Purohit |
| Topic | Author | Date |
| Signals encircling xtal. | 01/01/70 00:00 | |
| the issue | 01/01/70 00:00 | |
| Trace lengths and buffering. | 01/01/70 00:00 | |
| In that case I probably would not buffer | 01/01/70 00:00 | |
| Solid ground plane solves your problems | 01/01/70 00:00 | |
Thanks Kai. | 01/01/70 00:00 |