Polesse #13 17 октября 1999

Железо

Laboratory - On connecting external devices to the ZX-Spectrum.

              LABORATORY



     About Connecting external devices to

               ZX SPECTRUM

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(C) SSSR



   Here I want to tell you about, what
I ran into problems by connecting external
device to the ZX. Somehow came to me
KVAZAR and asked to pull up the modem to CDOS
his "COMPACT'u. It would seem simple:
looking at the board companies signals corresponding to the 
same on the modem and unsolder one to one. So I did. Turn on 
comp and waits for me the big bummer. EMS, as did not see the 
modem, and can not see, though of BASIC can be controlled. It 
turns out that it that every device I / O

in the computer, when activated signal IORQ,
considers it his duty to stick on the data bus every gag. 
Priority here depends on the particular circuit implementation. 
In "COMPACT'e" queried Kempston - joystick in the company 
"SKORPe" in 1994 - the port FF, even in some comp get underfoot 
AY. Only two companies among those that fell into my hands for 
the improvements, behave decently. Somehow, one of them was my 
signature "SCORPION", 1992, vypuschnny one of the first.


   The point here is this: if you select some external device, 
it should block all the others that they do not interfere with 
each other. This problem can be solved in two ways. 

   First - use the full (hard)
decoding. However, not always convenient
model for same-modem dozen other diodes or several buildings 
shallow logic moreover, as yet to a wide loop, overloading the 
address bus. Therefore preferred the second option - to lock 
the I / O signal IORQGE. To do this, you must enter it in the 
complex (where it's not). Here again there are two options.


   The first - to pick off 20-foot processor
from all other compounds, and solder in a gap resistance of 
430-820 ohms (selected experimentally before disappearing 
Gluck), as done in the "SCORPION'e" and "KAY".


   But it's better to do it differently, though for
This will require an element 2ILI (LL1).
If the board is free - it can be
use, otherwise the solder will have a chip K555LL1 second floor.


                 D1-K555LL1


       IORQ> 'to the rest

                           > Scheme

     IORQGE>


               /

                   2.2 to



   If an external device active
is low, such as 6-I
KR580VV55 foot in the scheme of the external port or
4-th leg K561LN1 in the scheme CDOS-modem, then
need to select the signal from input proinvertirovat and apply 
for IORQGE. This is easiest done by placing an inverter on the 
transistor KT315. If the external device is the active high 
level, the signal choice immediately throw at IORQGE.



                       By ___ +5 B

   __ 1k /

   CS ____ B | / KT315 (n-p-n)

      > ____ | <-----------
                     | \

          470 / E \ ______________

                                 IORQGE



   Strange that this does not say citizens of Minsk, which I 
ring up after the first unsuccessful attempts to pull up the 
modem, for hard to imagine that among the tens of

computers to which they connect the modem, did not find those 
in which there would be no such problems. Well, okay, Whatever 
it was, I'll be glad if anyone, this information can help you. 


   And yet, like, say a few words to the now-defunct St. 
Petersburg firm CREATE SOFT and LOGROS.



    One of these days I connected a controller
kempston-mouse to COMPACT'u. According to the original 
instructions wired system connector and redid the mouse, as 
described ZX-FORMAT-5. Turn on the computer and run the test. 
Observed such a pattern: regardless of the direction

movement of the mouse, the cursor moves only in
one side (or right or up), the only joy that the buttons are 
pressed. And when off the mouse cursor twitches,

as obdolbivshiysya. Again began to think what
here it. Scheme on the controller is not well
although chips are not erased. Considering
diagram of the controller in the newspaper OPTRON-13, drew 
attention to two trigger K561TM2, standing at the entrance. The 
product is from CREATSOFTa none found. Outputs with the mouse 
primed directly to the inputs of the counters and because of 
their high sensitivity, the controller responds to false 
positives and can not correctly determine the direction of

account. Therefore it is necessary to burn on
Controller second floor TM1 or TM2, and
also underpin inputs Xa, Xb, Ya, Yb resistances of 10 ohms to 
+5 V to When disabled the mouse cursor is not twitching.

In addition, the controller or in the instruction
were mixed on connection between a
two signals ...


   It is interesting to put yourself in the ordinary user, 
usually poorly versed in the gland. He goes to the firm buys 
controller for a decent price of about $ 10 and receive 
assurances that everything is in order, works great, you only 
need to connect properly and rulis myshoy health. He connects 
the controller and watch about the same now as it was I did. 
Naturally, he goes to the company, changing the controller, 
once, twice as long as it does not bother firmacham and they 
would say that either it connects properly, or comp buggy, or 
mouse is not in order, if at all, nothing say or even sderut 
five bucks for a supposedly finalizing company or for the 
connection ... 


   These are the reflections. Those interested in
details on connecting various external devices to the Speccy, 
please call me at phone in Gomel: (0232) 50-31-61, ask Sasha or 
write to Editorial newspaper.