Den Thu, 2 Nov 2017 12:49:34 -0500 skrev Jim Brain <brain@jbrain.com>: > On 11/2/2017 9:52 AM, Mia Magnusson wrote: > > > > Is there really more than sending 8 clock pulses and drive the data > > line? Of course with the correct polarity of all stuff e.t.c. > It's less a about when to send the $ff. and more about when *NOT* to. > > And, sending the $ff is trivial. It's watching for the $ff indicator > on the computer side * 8 ports at the correct time, and then ignoring > other $ff signals at any other time. > > Again, it's not insurmountable, but you either need to build 8 sets > of TTL logic to correctly watch for the indicator on the 8 incoming > ports (and ignore any other time), you need to use a microntroller > that can watch the 8 CLK lines at the correct time, or you need to > implement the functionality in a PAL/GAL/CPLD. I found that a 16MHz > uC could not satisfactorily watch the CLK lines for activity, and I > had no desire to bulk up on TTL in the board, so I decided to learn > Verilog so I could implement the required functionality. How big/small is the risk of a computer sending something else before pulling ATN? If I understand correctly there shouldn't be anything sent. Therefore we might get away with just detecting something similar to this activity. Although a discrete solution would grow to a really big card, it could probably be detected with a serial in parallel out shift register, an 8-input nand gate (7430 iirc), and some timing circuit that makes sure that there isn't too much time between FF and ATN being pulled low. AFAIK it's only C128 (and atleast in theory C64 modified to work the same way as C128) that can do burst mode. Most users would probably only need burst mode compatibility on one or two ports. Also most users would probably not need all 8 ports, but limiting the number of ports in general might nog save much. It's rather obvious that the number 8 stems from what was easy to achieve with standard logic IC's :) -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies. Message was sent through the cbm-hackers mailing listReceived on 2017-11-02 20:01:38
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