Sinclair ZX81, Assembly Instructions Manual, Page: 21 / 43

Vhen all la well, Insert the diode and transistor the correct way around
as indicated in fig 1 . Finally insert the 4 ICs, again consult fig 1 for
polarity ICQ Inserted the Wrong way
artpund will almost certainly ba destroyed when the board IB plugged m so be
particularly careful here
Vhen construction ifl complete, plug in the board, and apply power to the
ZX Again the machine should operate as normal if not, check that the ICa
arq correctly inserted, and that there are no board shorts.
Once the board la functioning there are many tests and experiments that
Bay be performed including full freo^jency range" audio output See arti
clSB m Personal Computer World (October and November 1981), But here are BOme
introductory notes!
Output Fort
Connection to the port are shown in fig 2 There are 8 separate output
channels, and they may be controlled with a single poke statement! POKE 25000,
X for the ZXBQ or POKE 11000,X for the 81. X may be any integer between 0 and
255 With £=Q all output linaa are eet to logic lov, whilst 255 Bate them all
high To set any one channel high while leaving the remainder low, the follow-
ing valuaa should be used:
POKE VALUE (X) CHANNEL ACTIVATED
1 0
2 1
4 2
8 3
16 4
32
5
64 6
128 7
Thus the command POKE 25000, 16 (or POKE 11000, 16 on the 81) will set channel
4 high, leaving the others low Setting a high output on a number of channels
ia achieved by combining the data Thus POKEing the value 12 (=9+4) will set
channels 2 and 3 high
When a channel goes high it may be used to trigger a variety of devices.
Fig 3 shows LED indicator lamps attached to channels zero and one To light
these, execute POKE 25000, 3 (or POKE 11000, 3 on the ZX81)
Belaya may be controlled from each channel as shown in the application
notes, and sound output may be produced by connecting a high impendence (eg 65
ohm) loudspeaker to the ouput plug aa In fig 4 The following programs will
produce blips on the loudspeaker
10 EB« ZX80 BLEEP 10 HEM ZXB1 BLEEP
20 FOR A = 1 TO 100 15 FAST
30 POKE 25000,1 20 Kffl A = 1 TO 100
40 POKE 25000,0 30 POKE 11000,1
50 HBCT A 40 POKE 11000,0
50 NEXT A
To produce a higher frequencies and more interesting effects it ia necessary
to uee a machine code subroutine, and complete programs for this on both 2X60
and 81 are given in tha applications notes, and in PCW.
• B»«_»r-iiAi%_MVIA*l ll~» R-IIVH I fc=l I .^
17 BURNLEY ROAD
LONDON NWIO IED
Telephone OI-452 I5OO OI-45O 6597
IBS 2X80/61 Pom - KOTES TO ACCOHPAHY KIT
The following is provideds-
1 Double Bided FOB
4 IOB labelled 1 - 4
1 Diode (IN9-14) (glassy)
1 Heslstor (IK)
2 Capacitors (lOOn?) (round and flat)
2 14 Pin Dil Sockets
2 16 Pin Dil Sockets
2 20 Pin Dil Sockets
1 23 x 2 0 1" edge connector
2 16 Pin Header Plugs
1 2S2926 (green) Translator
1 HAH pack extender card (ZX81 only)
Confltraction
Begin construction as follows! Insert and Bolder in the 6 1C Sockets,
putting in the largest ones first Next Bolder in the 2 3 way edge connec-
tor, but if the board is for use with the ZXS1 do not trim short, the wires
protruding through the underside of theboard, because these will be used for
connecting the RAM pack extender card, (this is not possible on the ZX80)
Hot* that the edge connector whould have a plaatio plug at pin }. Be very
careful not to bridge adjacent tracks when soldering this socket. To reduce
the risk of this you can leave unsoldered any pins that don't appeal to Join
up to a track on the underside of the board Insert the two capacitors and
resistors, and Bolder these
Next solder the through connections at all the remaining holes that have solder
pads on the upper side of the board except
EITHER the three marked «A" if the board is for use with a
ZX81 (note that the third 'A' le somewhat obscured by the
edge connector)
OH the two marked B if it la for a ZX60. The through connec-
tions require a piece of wire to be passed through the board,
end carefully soldered both sides before clipping off.
At this point, and before inserting the ICs or the diode and transistor,
plug the board into the ZX80/81, and plug the power plug into the computer
The cursor should appear, and the ZX should work normally If it does not,
there is a short circuit eomewhere on the board - probably between a pair of
adjacent tracks The short can be traced (after unplugging the board) using
a multimeter on the ohms range, or other continuity tester (eg battery and bulb)
- or you can Bsarcb. visually. If it io a solder bridge then you must reaolder
the point, but you Day find that you can ole.ir tha short by passing & small
screwdriver bl*-^ between the offending tracks.
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