The Story Behind the Development of the New TK87C51 Series

Tekmos is starting off the new year by releasing our new product line of programmable 87C51 microcontrollers. Designed as drop-in replacements for the 87C51 products formerly offered by Intel, NXP, and Atmel, these parts are available with program memories ranging from 8K to 64K, and in the PLCC, PDIP and LQFP packages.

The TK87C51 series is based on our 80C51 family that has been in production for years. When our original fab closed, we had to transfer the part to our new fab in Dresden, Germany. At that time, we decided to add flash support and additional RAM to the part which creates the 87C51Rx2 series. The ROMless parts remain as they were before, but now we have the option of adding flash to each part, using our stacked die technology.

There are a number of details in adding the flash. First is interfacing the flash to the processor. The 87C51Rx2 family runs from 3 to 5 volts. Our flash memories run off of 3 volts. So, we have to put a 5V to 3V voltage regulator on the die. The voltage regulator is more complex than normal because it must be able to handle the rapid increase in the flash supply current when the device is being programmed.

The second detail was determining how to program the flash. We made the part so that it emulated the original part during programming. This meets customer needs, but we have additional manufacturing requirements. Our flash has 512K bytes in it. We need either 8K, 16k, 32K or 64K bytes for program storage, depending on the type of 87C51 we are replacing. The control for the program size is kept in flash, along with the security bits and clock speed. We have had to add a special parallel programming mode that lets us have access to all the bytes in the flash. We have a third programming mode, ISP (In System Programming), that could also allow the part to be used in 89C51 applications.

A third flash design issue was adding circuitry that read the flash right after the termination of reset and then downloaded the configuration byte, security bits, and speed select.

And speaking of reset, we modified the reset circuit by adding a filter that prevent short glitches on the reset line from resetting the part. We have seen noisy applications with the 80C51 where this was a problem, and wanted to prevent that problem from occurring on the new 87C51 devices.

With these changes included, we made silicon, and now have the parts ready to sample.

Date

2018-01-15