Report Generator Board
ENER-Z Company
PO Box 635
Port Washington, PA 19034
FEATURES: Real-time clock, A/D, I/O Ports, parallel printer interface
PRICE: US$ 89.95 A&T, $59.95 kit
If you could buy only one peripheral which would let your ZX/TS communicate with the real world, Ener-Z’s Report Generator just might be it. The board’s features include a real-time clock, analog to digital interface, input/output ports, and a Centronics printer interface. All those features, and the under $90 price tag, sounded like too good a buy to pass up to me, especially since one or two of these features alone would cost more than this board from most other vendors. Does the R.G. deliver? Let’s take a look.
Physically, the R.G. board is 4″ x 6″ and has a cleanly designed layout for its 16 ICs and assorted passive components. Construction is professional, with few jumpers, plated-through holes, and sockets for the more critical ICs. An on-board regulator is supplied; this helps keep your ZX/TS’s internal regulator cool. A battery holder is provided for the real-time clock (RTC) and most of the offboard tieins can be made using standard DIP (dual in-line pin) headers, which are easy to obtain and inexpensive. In most uses, extra ground or 0 volts lines are required. These fall between the active lines and help keep down the effect of transients (glitches) in your ribbon cables to the real world, The board plugs onto the ZX/TS expansion port and a “through” edge connector is provided for other addons (e.g. RAMpacks).
The heart of the R.G. board is a Z80 PIO (parallel input/output) chip. Through clever use of an internal data bus (on the R.G. board) Ener-Z has expanded the capabilities of this simple chip to allow it to address what, in effect, are more than five separate port configurations instead of the usual two. Two versions of the R.G. are available, one has all its software on a 2716 EPROM (mine is this type,) the other has the driver software in RAM. The RAM version is required if you already are making use of the 2800-2B00h area where the EPROM would normally reside. All functions on the R.G. board are accessed with USR calls to the appropriate subroutines on the EPROM, which in turn executes the I/O functions,
An OKI MSM-58321 clock chip provides the year, month, day, week, hour, minutes and seconds for the RTC. With 3 Nicad batteries installed and the clock setting software (supplied as a listing) entered, you need only enter the correct time once and your ZX/TS will always know exactly what time it is. This is especially helpful if you want your computer to perform certain I/O functions at specified times.
Eight-bit input and output ports are provided by a 74LS244 buffer and 74LS373 latch, respectively, The inputs can monitor digital signals in the TTL range (0 or 5 volts.) Real-world signals can either be directly coupled to the buffer lines (e.g. simple switches) or coupled through conditioning circuits (e.g. relays, optocouplers.) Outputs are TTL compatible, although load-carrying capacity is only moderate. To drive a large fanout or heavy load, you’d need power amplification/ buffering stages (e.g. optocouplers + triacs to run 110 VAC circuits.)
The analog converter section of the board uses a National ADC0809, eight-bit port, eight-channel input, to convert real-world signals into their digital equivalents. As an example, a measurement of 50 means that the ADC input is seeing about 1 Volt DC. With 8 channels, you can monitor the status of 8 separate analog devices. Typical uses here include monitoring proportional-type joysticks (paddles,) thermistors, photo-voltaic cells, peak-detector circuits, and pressure transducers.
Up to this point we’ve seen how this board can tell you what is happening off-board (digital input and A/D), know when it’s happening (RTC) and even perhaps do something about what it sees (output). Now we’re at the stage where, perhaps, you can see how the board got its name. The unit can also generate physical reports about what’s going on, this time by using its final feature, a Centronics parallel printer interface. For this important, high-speed task, the PIO ports are used directly. Eight data lines transmit ASCII character codes generated by a look-up table in the EPROM. The EPROM effectively “overlays” the Sinclair ROM for this operation, allowing the support of Sinclair’s LPRINT, COPY, and LLIST commands directly, for the printing of the standard character set. Graphics are not directly supported, but special USR calls can produce a byte code which will produce other character depending on your printer’s capabilities. The overlay of the Sinclair’s ROM is done by overriding the ROMCS NOT signal when the printer commands are invoked.
The other two lines provided by the printer are STB (strobe) NOT and ACK (acknowledge) NOT. I used the interface with a Centronics 101 printer and Ener-Z says it works with Epson and should work with most other Centronies-standard printers. I agree, but suggest you include your printer type in any correspondence with Ener-Z.
After getting my R.G. board, I put it through its paces, on and off, for over a month. The RTC lost only a few seconds, and I hooked up switches (joystick, actually) to the input ports. I’ve used the output ports, all eight lines, with two offboard chips to drive a 3 digit, 7~segment LED display [Reported in Vol, 2/2 -ed.] This setup lets me see measurement status without turning on the TV. The A/D converter measures some resistance circuits I’ve set up quite accurately, and I’ve even tied it into a thermistor and gotten a fairly good thermometer, accurate without amplification to about 2-3 degrees F, To get the printer interface working, you’ll need to make up your own cable. You can get everything you need at Radio Shack or a number of the mail order houses. Try to keep your cable length under 8-10 feet in length.
lf the R.G., board sounds pretty good up to this point, make no mistake, it is, However, it seems that nothing is ever absolutely perfect and there are some negative aspects to the board. Minor turnoffs which don’t really affect the board’s performance included a loose battery connector on my board, some “afterthought” pull-up resistors tacked on to ensure TTL-CMOS compatibility, and the lack of a case. Three more meaningful items, which might even affect your decision to get this R.G. board, do need mentioning. First is the somewhat hastily prepared documentation, While there is an excellently documented source listing for the EPROM, the supporting narrative on BASIC applications has quite a few typos and no page numbers, The 29 page documentation swings back and forth between the EPROM and RAM-based USR calls, and while a mini-hex monitor for loading the RAM version (you have to enter this by hand) is provided, the hexcode listing is not. I’d suggest that Ener-Z% either prepare two separate versions of the documentation or one complete and comprehensive dual version. I think the average user will be able to use the board, but straight BASIC programmers (i.e. who don’t use ML and have little hardware knowledge) may find they’ll have to make a call or two to Ener-Z for guidance. I have found them most helpful on the phone.
The next complaint is that we’re not told explicitly in either the advertising or the documentation, which port locations are used. In the case of the R.G, board, with a little digging, the source listing does indicate addresses 01, 03, 05 and 07. However, a quick look at the board’s partial decoding will show you that ANY odd numbered port below 80h will respond to the I/O calls from EPROM. Keep this in mind if you have other I/O mapped peripherals.
The other significant “flaw” with the R.G. board has to do more with the “nature of the (Timex/Sinclair) beast” than with the board itself. As you probably know, the ZX/TS cannot directly address I/O ports. In order to do so, then, we just jump to a machine language routine in FAST mode, and consequently lots of blank screen time and “flicker.” I probably wouldn’t have thought this to be a significant problem if I hadn’t seen JK Audio’s 310 board. While this board costs about as much as the R.G. and has fewer features (I/O ports and clock only,) it uses memory mapping to accomplish its I/0 function. I don’t feel the R.G. board should be downrated on function because of the difference, only that users should be aware of a need for a little more effort required to produce good-looking screens with the R.G. board.
To more than make up for these little flaws, the R.G. offers its high reliability, numerous features, low cost and some bonus features not mentioned in its documentation. The board nominally has one 8-bit input and one 8-bit output port, You could conceivably stretch these, with some off-board multiplexing, to 64 each. How? Schmitt (or comparator) conditioning of signals fed to the A/D converter could give you 8 more digital input lines. Also, the printer port has 8 bits, this time with handshaking, There are other such combinations which you could implement with a few ICs to suit your particular application. A final extra bonus is that about 180 bytes of the EPROM are not yet programmed, Using sufficient care, and an EPROM programmer, you could use this area to add your own special USR toutines to the board.
On balance, I found the R.G. board an excellent value and perhaps (next to my $39.95 Timex) the most cost-effective computer purchase I’ve made. If you need any two of the board’s features, I recommend buying it. I’ve given this board a hard-to-get 9.9 on my price-for-value scale. A “10” could be obtained if the RAM-driven version were provided on tape,and documentation cleaned up a little. Ener-Z has done an outstanding job with its first entry into the ZX/TS peripherals market. As a suggestion for further items, some detailed I/O applications (perhaps collected from users) could be provided and even hardware (e.g. temp probes, light pens, etc.) described or made available. [If you have created any little add-ons for this or any other applications boards, let us at SWN know about it. We will let others know.-ed.]