storkus@arrakis.nevada.edu (Mike Storke (N7MSD)) (02/20/90)
You know, if you build a buffered cable like you say, how are you going to switch between 4 or 5 devices that all require the same I/O lines? The disk drive and RS-232 pak can't work at the EXACT same time, they must be multi- tasked. Please, how are you going to do that with a * (best visual interp.) cable? Mike
djh9381@ultb.isc.rit.edu (D.J. Halko) (02/22/90)
How can you construct a buffered cable? YOU CAN USE and RS232 and DISK controller at the same time... at the same time as using a B&B also... they are all at different addresses... just yank out the ROMs and you will be in good shape... if you have a B&B autoboot PROM, then yank out the DEB and RS232 Pak ROM (not much use for them under OS9... there is nothing you can't run in OS9 that you can under DEB now anyway! (except some coco games... but OS9 has its share now.) The ROMS are the only addresses that conflict... Now, how to build one... I forgot the bus structure of the CoCo - I'll have to get a tech manual again... just have to stick some buffers over the data and address lines and have them tripped using the READ/WRITE line (I think.) Someone mind corecting me if I am wrong? As long as you are not doing the internal switching, the circuit should be a snap. Just a pain to wirewrap! ;-) Dave
news@uflorida.cis.ufl.EDU (USENET Master) (02/22/90)
From: se@beach.cis.ufl.edu (Sina Eatemadi) Path: beach.cis.ufl.edu!se 1) Build your own MPI: This would be more trouble than it is probably worth. You could, however, build a Y-cable with datadate/address line buffering and slot selection. Get the service manual for Tandy part # 26-3024 2) Buy a third party MPI. Two are currently advertised in the Rainbow. 3) Build a double or triple Y-cable: These cables are fairly easy to make but you must keep a few things in mind. Keep the cable short (under 3 inches), otherwise you'll get bus timing problems. Only have one active ROM on any device plugged into this cable. pull any RS-232 pak ROM's, hard drive autoboot Rom's, etc. WATCH FOR HARDWARE ADDRESS CONFLICTS. These are fun to deal with. Most (all?) CoCo hardware is not fully addressed decoded. The Tandy disk drive controller is about the worst. The RS-232 pak is decoded down to 4 bytes and will work with just about everything. Lastly, contrary to what someone posted earlier, the B&B interface will NOT plug into a Y-cable unless it is modified. Even if the autoboot ROM is pulled, the CoCo still senses 'something' at the standard ROM addresses ($C000+) from the B&B. This conflicts with the disk controller rom and will cause the CoCo to lock-up. There is a hardware mod for this problem available from Chris Burke. Hope this is of help to everyone... latr ChrisM se@beach.cis.ufl.edu