EMBED THIS PC part 3

THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

EMBED THIS PC

Lessons from the Trenches PART 3: Emulator to the App Test
by George Martin

Start ı The Program ı Real Mode ı Getting An App Up and Running ı Sources and PDF

In this series of articles about embedding a 486, I identified a laser light show as an application suitable for an embedded 486 project. The application continuously outputs data as fast as possible to a couple D/A converters. I discussed one DRAM device and AMDıs ELAN processors and covered many of the issues necessary to develop an embedded 486 project.

Last time, I left you with a table of connections that wire the DRAM to the CPU. I will continue from that point and detail the emulator, as well as discuss real- versus protected-mode software development.

EMULATION CHECK POINT

For emulation, I discussed an EPROM emulator and identified Grammar Engineıs PromIce and Paradigmıs PDREMOTE software as good tools for a low-cost, useful solution. Letıs explore this solution further.

By using a 29F040 flash-memory device for the startup (BIOS) code thatıs packaged in a standard 32-pin DIP format, I can use an EPROM emulator and plug it into the socket that replaces the BIOS flash device. (By the way, for the purpose of this discussion, Iıll use the terms flash memory and EPROM interchangeably.)

If your code is small enough, an EPROM might be suitable. EPROMs can be erased with UV light and reprogrammed. The flash-memory devices are larger, but they need to be electrically erased before theyıre reprogrammed, which ties up the programmer (see Table 1).

	DRAM 1		DRAM 3
		DRAM 2		DRAM 4

	Bank 0		Bank 1			Buffer

Signal	Low	High	Low	High
MA0	17	17	17	17	18	74LVTH244ADW	2
MA1	18	18	18	18	16	74LVTH244ADW	4
MA2	19	19	19	19	14	74LVTH244ADW	6
MA3	20	20	20	20	12	74LVTH244ADW	8
MA4	23	23	23	23	9	74LVTH244ADW	11
MA5	24	24	24	24	7	74LVTH244ADW	13
MA6	25	25	25	25	5	74LVTH244ADW	15
MA7	26	26	26	26	3	74LVTH244ADW	17
MA8	27	27	27	27	18	74LVTH244ADW	2
MA9	28	28	28	28	16	74LVTH244ADW	4

Table 1ıHere are the DRAM connections for the Elan SC400. As you can see, DRAM 1 and 2 share Bank 0, while DRAM 3 and 4 share Bank 1.

The BIOS EPROM contains the reset vectors for the CPU. At power up, the CPU vectors address the device, fetch the code, and execute. Your PC has the same sort of device. Code from the PC BIOS EPROM is copied into the DRAM for faster execution. The BIOS EPROM typically has an 8-bit data path and slower access time than the CPU and DRAM.

Also, if the BIOS EPROM is a flash-memory device, itıs possible to reprogram it in the field. But, no matter what the detail of your particular design, you can have full debugging access through the 32-pin DIP socket. The PromIce emulator plugs into the socket used by the BIOS device.

Before youıre ready to go, you need to make two extra connections to the hardware. First, the reset signal from the PromIce must go to the reset line of your system. The reset line holds the CPU reset, while PromIce loads the device contents. Secondly, the write line from the CPU needs to be connected to the PromIce. PromIce uses the write line to intercept commands and data from the CPU.

The PromIce emulator includes a LoadIce program, which loads or forces code into the EPROM. Now, letıs work on something to load.

Circuit Cellar provides up-to-date information for engineers. Visit www.circuitcellar.com for more information and additional articles.
For subscription information, call (860) 875-2199, subscribe@circuitcellar.com or subscribe online. ıCircuit Cellar, the Magazine for Computer Applications. Posted with permission.