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Circuit & Design Ideas

Interestmg Circuit ideas from readers and technlcal literaturę. While this materiał has been checked as far as possible, the circuits have not been built and tested by us. As a consequence, we cannot accept responsibility, enter into correspondence or provide constructional details

SWło

SWlb

ci

SO.T.

0 00Ł7_UF

V SYNC IN o-FRO*

VlOEO FADER IC lb PIN6

<Rvlal +-SS00W O* 5 LIN

SW2

TRANSPOSE

swic

mod€

<H7pF ^1 - 41: ^	P
■ u^# vSk aĄĄ, X	BLANKING OUT to
	VIDE0 FADER
0C337	Q3b

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a

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<Rvib -+-<SOOk C* < LIN

SW1-) : vertical wipe

SWł-2: HORIZONTAL WIPE SW>-3 = CORNER WIPE

(Top lefl - bottom rtgUj

SWi-4: CORNER WIPE

I Bot tom teft-top right)

H SYNC IN o—

FROM

VlOEO FADER IC to PINII

«SV 0V ICi:tS38-PiN »6 S 1C2: L077-PIN U 7

Wipe effects for the video fader

This Circuit is an add-on enhancc- This w ment for the EA Video Fader of Janu- vertical > ary 1986. It givcs morę variety to home puls of I video editing, by adding wipe effects to nectcd d the fade effect originally provided.    SWlc. H

IC1 is a dual monostable, triggered ibility. by horizontal and vertical sync pulses When extracted from the Video Fader. RV1 IC2d ch; sets the monostablc*s output pulse verting g width, and hence the position on the tion on screen of the blanked/unblanked transi- unblanke tion.    combines

This would give simplc horizontal and vertical wipcs if the O and O-bar out-puts of ICla and IClb were only con-nectcd directly to the four position of SWlc. Howcver IC2 allows further flcx-ibility.

When SW2 is opened IC2b, IC2c and IC2d change from non-inverting to in-verting gates. This transposes the position on the screen of the blanked and unblanked portions. In addition, IC2d combines the horizontal and vertical

blanking pulses to give a comcr wipe along one diagonal of the.screen.

To wipe along the other diagonal re-quires that, for one monostable: the di-rection of its wipe is reversed, and its output is inverted. This function is pro-vided by SW la, SWlb and IC2a.

Rl/Cl & R2/C2 are critical for best fit of the corner wipe, and they should be selected on test. First select C1/C2 with RV1 at maximum, then select R1/R2 with RV1 at minimum. R1 and R2 must not be less than 5.6k (IC manufacturer*s spec). No other compo-nents are critical.

Peter Prausc,    Or

Kewdalc, W A

Centronics interface for Apple 11+

This Centronics parallel printer interface is suitable for an Apple 11+ Computer. I havc also enclosed a listing of a suitable drivcr program.

A significant advantage of this card is that it is simple. I could not get convcn-tional cards to work on my Computer, so I* built this interface. I mounted it in a fibreglass box outside the Computer to save w i ring.

The interface should work with any standard Centronics interfaced printer. It allows software to send data to the printer and to initialisc the printer. It also adds an extra 1K of memory to the Computer in which to storę an interface program. The additional memory is in four pages which may be sclected by software on thosc pages.

For memory the interface uses two 2114 static RAMS (1K x 4 bits) which need no logie to conncct straight to the Apple I/O. A 74LS244 tri-state octal buffer is used to monitor the outputs of the printer (PE.BUSY, ERROR, SLCT, ACKNLG-bar). Thrcc of its inputs are not needcd and may be con-ńected to ground if no further expan-sion is desired. Logic is used to ensure that it is in high impedance State unless R/W-bar is high and Device Select is Iow.

For output to the printer, two latches are used, the control latch (a 7475 quad latch) and the data latch (a 74LS373 octal latch). The control latch has two bits going to the high address lines of the RAMS to select memory pages, and two bits going to the STROBĘ and INIT printer inputs. Logic is used to ensure that these will only be accessed when R/W-bar is Iow, Device Select is Iow and the correct address linę is high (AO for the control, Al for the data).

A summary of interface locations is as fol Iow s. These values are for slot two

only. If the card were used in other slots, the locations would differ.

0)90 — load from here for printer status byte

0)91 — storę the control byte here 0)92 — storę the data byte here C100 to C1FF — RAM interface memory (selectablc)

• Thus to print a character, the hex codę of the character is fed into SC092, then $0)91 is accessed twice, once to send STROBĘ Iow, then once to send it high again. To make surę tl at the printer is free for the next character, the program must wait until BUSY is Iow (it can check BUSY by loading from $0)90).

The listing is of a vcry simple driver routine, but, with 1K of memory at the programmer’s disposal, a much morę elaboratc routine including a screen dump, Hi-Res graphic dump and special BASIC list routine could be constructed (I have madę these separatcly, but I see no need to include them in the routine).

ELECTRONICS Australia. September 1987