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COMPUTER BITS BY DARREN YATES A low-cost emulator for Zilog’s Z8 microcontroller Creating your own microcontroller projects is not as hard or expensive as you may have thought. GEC Electronics now has available Zilog’s new low-cost emulator for their Z86C04/ E04 & Z86C08/E08 8-bit microcontrollers. We take a look at the IceBox to see what it can do. Microcontrollers either have you interested or totally bored but whatever your persuasion, they represent the “now” generation of electronics. They are more often than not seen as little “do-everything” boxes capable of solving just about every circuit problem. Now while that may be the case for industry, for the aver­age hobbyist they are still pricey, particularly the programming systems. Let’s take a look at the pros and cons. Programmer vs Emulator It used to be that code was hand-programmed into the chip but now all programming is done via the PC, which can make for a much more convenient approach. The convenience depends on what path you follow. While microcontroller programmers are relatively cheap (ie, around a few hundred dollars), they do present someth­ing of a problem. If you are debugging code and trying to fine-tune your project, you are forced to erase and reprogram your EPROM microchip each time you wish to change the code. This may sound fairly simple but it is a time-consuming exercise. This is also an expensive approach. Most distributors will tell you that their micros are cheap but that’s so long as they’re only talking about One-Time Programmable (OTP) devices. When you start to talk about the EPROM versions, which you need if you only have a programmer, the price skyrockets – you can expect to pay 5-10 times the cost of an OTP part! In real terms, this could be anywhere up to $35 more. The better alternative is to have an emulator. This is a board which can actually emulate or take the place of a chip. The board has a socket and a cable is connected between it and your circuit. The cable has a header on it which takes the place of the chip in your project. You now simply program the board to act like the chip and you no longer need the expensive EPROM part. The beauty of this system is that you can modify your code and check it instantly – there’s no waiting to erase the UV PROM in the chip which means that you can get your project up and running a lot sooner. The IceBox The register windows allow you to not only see all registers at a glance but also to edit any one by simply wiping over the register you wish to edit & typing in the new value. The ASCII equivalent of that code is displayed on the right. 62  Silicon Chip So what’s so good about Zilog’s IceBox? Firstly, it is low cost. For an emulator from most other micro­ controller manufactur­ ers, you can Zilog’s IceBox emulates the Z86C04/E04 & Z86C08/E08 devices & costs just $285 plus tax. It comes with two manuals which include application notes & the software is designed to run under Windows. All you have to add is a 9V DC power supply & a DB25 serial cable. can quickly compare code from two different applications as well as open multiple windows. You can open a memory map window as well as output port status windows – in fact, you can open every option available at the same time if you so wish. Thirdly, the Zilog Z86E04 chips which it emulates are very competitively priced at around $2.75 each in quantities of a hundred. In OEM quantities, the masked-C04 part price can be as low as $1.20. This rises to around $4.55 for one-off but it is still quite cheap when you consider what they can do. It will also emulate the Z86C/E30 and 31 devices (among others) which have more I/O lines. The IceBox will run quite happily on an old 286 PC but Zilog recommend that you use a 386 PC to get maximum performance. You’ll also need at least DOS 5 and Windows 3.0. There are two manuals which include applications notes and ideas, as well as code examples to get you going. All you need to add is a 9VDC 500mA power supply, a serial DB25 cable and the ideas. Now while the IceBox emulator is well worth a look, what about the devices themselves? The Z86E04/08 This shows both the code & data memory windows. Again, each one is shown in hexadecimal format (which can also be switched to binary). The data memory has no meaningful data in it & displays its default settings; ie, FF hex. Both can be edited by wiping over the particular byte & writing in the new value. expect to pay over $700. The IceBox is available for only $285 plus sales tax, and that includes a sample chip and all software. Secondly, the software itself is well designed and runs from Windows. The software programmer is very well written and is much easier to use than most DOS-based programmers. By operating from Windows, you The Z8 micros are 8-bit standard instruction code set devices but they have a very high proportion of input/ output (I/O) lines compared to the number of device pins (14 I/O lines for an 18-pin package). However, some of the more unusual features are within the chip itself. The Zilog range starts with the Z86E03 which has 512 bytes of ROM and continues through up to the Z86­ E63/64 which has 32K of ROM. I/O lines also can range from 14 for the smaller devices up to a whopping 52 for the Z86E64. The particular OTP devices of interest are: (1) the E04 which has 1K x 8 of read-only memory (ROM) and 124 x 8 random-access memory (RAM); and (2) the E08 which has 2K of ROM and 124 x 8 RAM. Each of these bytes of RAM is individually addressable so you don’t need to waste time working through an accumulator to get to a particular piece of data. Another good feature is that all software is transferrable to other members of the Z8 family. This makes it easy to upgrade from one device to another to suit your particu­lar needs. January 1995  63 Each device has two comparators which can accept analog signals and produce a high or a low, referred to a common exter­ nal reference voltage. This reference voltage can be anywhere between 0 and 4VDC (the supply voltage is 5VDC). What this does is make it very easy to interface outside analog circuits with the micro. The two on-chip comparators also allow you to create anal­og-to-digital converters (ADCs). Since eight of the 14 I/O lines are arranged into an 8-bit register address, you can easily pro­ gram an 8-bit digital-to-analog converter (DAC) and create a fairly quick 8-bit ADC using the microcontroller as a successive approximation register. The comparators can also link to internal program inter­ rupts which allow you to tell the micro to execute a certain portion of code upon receiving an external voltage level of some kind. This should give plenty of scope for experimentation. Timing For timing considerations, there are two on-board 8-bit counters, both of which run as a function of the main clock but one can also be programmed to work from an external clock source. This can be very handy if you’re working on a frequency counter, for example. Each counter has a 6-bit programmable prescaler to allow you to define a start position. This is useful for working on time-critical applications where you want a specific time to pass before executing some program branch. These counters can also be linked to internal interrupts and the current value of the counter is available in a specified register which can be read at any time. They are also reasonably fast, with the E04 capable of clocking at 8MHz and the E08 at 12MHz. Current consumption is in the order of 5-10mA, depending on the device, application and speed. Each device also has two sleep modes; one turns the device off, while the other also turns the main clock off. In this latter mode, current consumption falls to just 1µA which makes them entirely suitable for battery operation. By programming one of the external interrupts, you can easily wake the device back up again, even from this almost “dead” position. Both devices have power on reset, which starts the 64  Silicon Chip If your code isn’t working quite write, this is where you come. The debug window allows you to see each line of code and allows you to step through the code by any number of lines, which you can specify. The trace code box displays each line of code executed after its completion. You can also set break points though the code to find a particular error condition. Downloading hex code from the PC into the emulator is easy. You simply click on the DOWNLOAD option and you are presented with this screen. When you click on OK, the code is automatically loaded. The file format can be in either standard INTEL hex or binary. micro and enables it to begin executing code from location 000C(hex). OTP capability The E04/08 OTP option allows you to mass-produce low cost proprietary software fairly easily and, most importantly, these devices can be ROM protected. This feature enables the programmer to lock away the code so that it can’t be copied. Overall the Zilog IceBox emulator is a winner. It brings together a low-cost emulator system with a good all-round micro from one of the oldest manufacturers in the game. It certainly is the lowest-cost, most efficient programming system I have yet come across. For $285 + tax, it is excellent value for money. The package includes cross assembler, graphical user inter­ face (GUI) software and object utility files, as well as an emulator operating manual and a Zilog technical reference man­ual. For more information on the Zilog range of devices, contact Russell Lemon at GEC Electronics in Sydney. SC Phone (02) 638 1888.