DK'tronics Clock (Amstrad Computer User)DK'tronics Clock: Join the fourth dimension (Amstrad Action)Zwei in einem (CPC Magazin)
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Going like clockwork

A device which can remember the time when your computer is turned off is really useful. Rupert Goodwins joins the Campaign for Real Time. In the good old days, very few people knew about computers. Anyone who actually owned a micro could stun a cocktail party into awed silence by merely mentioning RAM or hinting at address bus width. Now, thanks to Amstrad and Sinclair, it seems that if you haven't got a modem, disc drive and NLQ printer you aren't worth inviting to the mendicants'meths bash under the railway bridge.

Fear not. The upper hand can once more be gained, thanks to DK'Tronics'new add-on. Just drop the simple "Oh, haven't you got an RTC yet?" followed by "Real time clock, of course." into the conversation and win every time. Real time clock is a bit of a strange concept. The jargon term Real Time covers a lot of nebulous ideas in the computer industry. Military types use it for machines that pretend to do things as if they were really happening, like flight simulators. Banks use real time to talk about electronic transactions that take effect within a few minutes, rather than being saved up until close of business. DK'Troniks Real Time Clock is a bit simpler than that: It's a clock that knows the real time -the hours and minutes stuff.

This might seem a little odd. Most clocks that humans use tend to work in minutes and hours, from sundials to the latest Yingtong 200m water resistant alarm chronograph with geiger counter. Computers have different needs, and thus different clocks. There is one master clock inside a CPC 464/ 664/6128 that whizzes along at 14 million ticks a second. It's used to time calculations and TV pictures, and the TIME variable that Basic users can see is generated by dividing it down to 300ths of a second ticks. As it (like everything else in the computer) gets set to zero when switched on, there's no concept inside the computer of "real" time, like 21:53:37 on May 14th, 1987. It only knows that it's been 165231 lots of 300th second ticks since it was last turned on. Not terribly useful to the poor old user.

What would seem to be needed is a wrist watch for your Arnold. Like the Yingtong it would need a battery, to tide it over when the computer isn't turned on. It would need some way to set up the time, like the Yingtong's 14-function buttons. And it would be pretty useless without the wherewith-all to read the carefully set-up and maintained GMT as it trickles away. The DKTronics Real Time Clock is that wristwatch.

The clock, looking more stylish than most peripherals in its angled black case, plugs into the expansion bus at the back of the CPC. It has a through connector for any other add-ons in your possession, which wins it points in profusion from this reviewer. There's a joystick-style connector on one side, and a small hole at the back in which can be seen glinting a small brass screw. A peek inside reveals a rechargeable battery, five chips, a quartz crystal and a few odds and ends. The battery keeps the clock going for a few months between switch-ons, and recharges in a couple of minutes from the computer.

The brass screw allows a fine adjustment of the clock in case it gains or loses over a period of time. It isn't mentioned in the somewhat scanty manual, but the clock should be allowed to run for at least 24 hours between changes. The changes should be very small (about 10-20 degrees), and to be honest not many people will be upset enough by a second or two drift a month to want to bother.

The joystick style connector is a general purpose 8 bit input/output port. Hobbyists can use it to control robots, or read burglar alarm switches. With some programming to do with the clock parts, it could control tape recorders, radios and other timeable devices. Everyone else can ignore it, it won't bite. Most of the hard clock-type work is done by one of the chips, the snappily-named HD146818. This has your actual clock inside, plus a bit of RAM and a few extras such ias an alarm circuit. It can also be found in Amstrad PCs and IBM AT computers, so you're in good company. The computer talks to it via the software supplied with the package. This comprises three programs; RSX.BAS which loads RSX.BIN, RSX.BIN which adds eight new extensions to Basic, and CLOCK-.COM, which allows CP/M+ (128k RAM owners only) to use the RTC.

The extensions are all fairly obvious. |ASKTIME and |SETTIME (nothing to do with when to feed hounds) read and set the time respectively. These all use year, month, day, hour, minute and second values in that order, so to set the RTC to the time mentioned earlier you'ld type |SETTIME,87,5,14,21,53,37.

You can omit as many of the parameters as you like, but you have to fill in all the settings after the one you want to set. So you can set just the seconds, or hours, minutes and seconds, but not just the hours or the year. All the computer knows is that the last setting in the list is seconds, and it works it all out from that.

BARASKTIME reads the time into a set of variables in the same order as |SETTIME set it up in the first place.

Moving a little up the scale of horological sophistication we find the |ALARMON and |ALARMOFF commands. The first works by setting a Basic F% sets F% to -1 at 11:05:05, for example. It is also possible to make the alarm go off every hour -no prizes for guessing what |ALARMOFF does.

The final time-related commands are |TIMEON and |TIMEOFF, |TIMEON,COLUMN,LINE,RATE displays the time at COLUMN,LINE on the screen, updating it every RATE/ 50th of a second. This only really works from Basic, as games tend to do very odd things with the screen. However, a few hours happy experimentation can be had finding out what happens with all those odd blobchasing programs. |TIMEOFF stops the time display.
The last two commands are there for the hackers among us. A word of explanation first - the clock chip is designed to look to the computer as if it was memory. Only 64 bytes, it must be said, but the computer already has a full complement of memory, so DKTronics has had to use some powerful magic to shoehorn in even 64 bytes. This means that PEEK and POKE won't do any good, so the commands |POKERTC and |PEEKRTC allow the more crazed user to access all 64 bytes.

These bytes are often used to store colour settings and other customis-ations for your software. As the contents stay even when the clock is unplugged from the computer, a possible use would be to hold a password without which the computer won't start up. That way. you could keep sordid details of your private life on disc, secure in the knowledge that with the clock hidden away nobody else could ind out the awful truth by tampering. 3ut it would take a bit of programming.

CLOCK.COM is run from CP/M. It sets the CP/M system clock to the real time clock's time, and allows the computer to mark anything saved to disc with the date and time - a procedure known as datestamping. Here lies the true usefulness of the product, because there are serious uses for this gizmo. Because by now the obvious question might be making itself felt - what can a £35 computerised clock do that a £1:99 wristwatch can't?
It depends on what you do with your computer. If it's just gamesplaying, then the RTC is not for you. However, serious users might just find it an investment worth having. If the computer is used for developing software under CP/M, say in C or assembler, then there are going to be various ver-' sions of the program being worked on floating about the place.

Most software developers try out a modification or bug fix by making a new version of the program, and keeping an old version just in case the modification proves worse than useless. This perfectly sound procedure spawns discs full of apparently identical software, and without datestamping it can be difficult to know which version of INVADERS.COM had that really meaty laser-zap.

With datestamping, it becomes easier to search for the version of two days ago, and just the sight of a program stamped 03:49 can bring tears to the glazed eyes of many a hacker. The same is entirely true of madmen who insist on writing reviews at (glances at wristwatch) half past twelve at night. Other software can be improved by an RTC; mail merge programs can often be set up to insert the current date in a document, but this is a chore to begin with, and dire indeed after the twentieth reset of the evening. It can also be handy with accounts programs to know when a certain data file was last modified: Datestamping tells you.

On test, the clock worked. What else can one say? All the nasty business about leap years and funny months is taken care of, and times can be in 12 or 24 hour format. I couldn't find anything really wrong with the hardware design; the battery charging circuit was perhaps a little too simple. Similar designs (as Acorn knows) have catastrophically failed in the past - it only takes one faulty component to destroy the battery by overcharging and only one extra tuppenny diode to make it much safer. But it's unlikely to go wrong anyway; just a thought for next time, dk'.

This is a serious peripheral for the serious user and hobbyist, who will find it seriously useful. The manual describes the technical bits of the interface and gives a couple of very minor application programs. It doesn't attempt to give any sort of idea as to the uses of the clock, or details of the chippery involved. But there's enough for the knowledgable to use it for real-time control of assorted hardware, or clever homebrew diary/appointment book software.

Some people might think that they won't rush out and buy it - instead they'll wait and get it for their birthday. After all, there's no present like the time.

Amstrad User July 1987

★ YEAR: 1987
★ CONFIG: 464 and 6128 only
★ PRICE: £34.95 (UK)


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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.