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 Hoepping Elektronik Design informs ...

Atmel FLASH-Controller
MCS51 microcontrollers, especially the standard types, eg. 87C51, do not really require state-of-the-art semiconductor technology.

Why do they cost so much then ???

One of the reasons is the expensive packaging. With a 87C51 you are mainly paying for the ceramic package with the quartz window. A 80C31 without EPROMs costs considerably less.

The alternative:

Microcontrollers with FLASH memory. FLASH is somewhat more advanced and expensive memory technology than EPROM. However, the additional costs are more than compensated for by the inexpensive plastic package.

AT89C51, AT89C52, AT89C55

These controllers are drop-in replacements for the types 87C51 and 87C52. Programs that have been written for such an 87-series controller can be programmed into a 89-series controller without requiring any changes.

However, Atmel does not just restrict itself to 87-series replacements...

AT89C55 in DIP40 package

small on the outside - large on the inside
AT89C2051-24PC in DIP20 package
(picture is enlarged)

AT89C2051-24PC

  • a complete MCS51 microcontroller in DIP20 or SOIC20 package.
  • 100% software-compatible to the 80C31 microcontroller
  • Data sheet in PDF-Format (246k)

system comparison: AT89C2051 to 80C31 with EPROM 27C16 and latch 74LS373
AT89C2051-24PC 80C31, 27C16, 74LS373
  • 2k FLASH internal program memory
  • 128 bytes RAM
  • Clock frequency: 0..24MHz
  • 15 free programmable IO-port (port 1 and bits 0..5 and 7 of port 3)
  • UART, 2 timers
  • Analog comperator. P1.0 and P1.1 serve as inputs for comperator; the externally not available port 3.6 serves as output for the comperator.
  • programmable read protection
  • 2k program memory in external memory
  • 128 bytes RAM
  • clock frequency depends on type
  • 16 free programmable IO-port (port 1 and port 3)
  • UART, 2 timers

Functioning hardware for AT89C2051-24PC consists of the controller with a crystal and two ceramic capacitors, an electrolytic capacitor between Vcc and RESET and a 100nF bypass capacitor on the supply voltages.

The 80C31 has more IO ports, although ports 0 and 2 are already used for connection to the external program memory. This leaves only ports 1 and 3 available for the application. Apart from P3.6, these are the same ports that are available with the AT89C2051-24PC. All other features, such as eg. timers, serial UART, idle mode and powerdown mode, are 100% compatible.

The AT89C2051-24PC also features an analog comperator. It has an static processor core, ie. there is no minimum clock frequency. the maximum clock frequency is 24 MHz. Of course the AT89C2051-24PC can also be run at 11.0592 MHz.

If more than 2k bytes program memory is required, type AT89C4051-24PC may be used. This device has 4k bytes memory and is identical in any other regard. Data sheet AT89C4051-24PC in PDF-Format from Atmel.
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