This is a frozen project. It is intended to provide authentic snapshot of the history with all the good things and all the things that could be improved.
The article was published in July 2019 in Czech magazine Praktická elektronika - Amatérské Radio. It is written in Slovak language.
It describes construction of converter for programming AT89Cx051 microcontrollers using an ISP programmer for AT89S51. I created this device for attending a contest at a secondary technical school where I studied. It had been stashed in a drawer since then until I decided to revive it. It was originally realized with SMD parts but for easier construction I modified it for use of mainly classic electronic parts. It supports erasing, writing, and reading of the program memory of AT89Cx051 and writing its lock bits.
Its purpose is the same as my previous construction has, but it uses a different principle.
The functionality can be split into two parts. The first part is between an ISP programmer and the onboard AT89S51 MCU. The programmer is connected to the MCU and the RST programming signal is used as an external interrupt source. When the firmware detects start of a programming operation using the interrupt, it simulates the real programming logic of AT89S51. However, the data is written/read to/from the FRAM memory connected to the MCU. The ISP programmer sees only a virtual AT89S51 MCU. In order for the real AT89S51 to be able to process the ISP programming signals in real-time the frequency of the SCK clock has to be fairly low. I tested it with 32 kHz.
The second part is between AT89S51 and AT89Cx051. After a programming operation in the first part is completed, an equivalent operation is executed in the second part. For example, if write operation to the virtual AT89S51 is completed, the data is read from the FRAM and written to the AT89Cx051.
The button controls the second part. Short press switches a direction of synchronization (up or down) between AT89Cx051 and the virtual MCU. Long press starts a synchronization in the selected direction. The synchronization means transfer of a data for AT89Cx051. If the direction is down, the long press starts write of data from the FRAM to the AT89Cx051. It the direction is up data are read from AT89Cx051 and written to the FRAM. From there it can be read by the ISP programmer. The direction of synchronization is indicated by the yellow LEDs.
This converted can be also used for copying program memory of AT89Cx051 without any ISP programmer connected using only programming operations in the second part.
During an ongoing operation in the first or the second part the red and the green LED are both on. After the operation is finished, only one of the two LEDs is on. The green LED indicates success, the red one indicates an error.
