With the new Commodore 1541-II and 1571 drives, Commodore introduced a new gate array called 251828. In this gate array further functions were included, which were still discrete in the “old” 1541.
This gate array offers functions not only for the 1541, but also for the 1571. Since I don’t own a 1571 myself, I could only concentrate on the part for the 1541.
Therefore this replacement is only executable in the 1541-II. Since also the pinout between the 1541 and the 1541-II is different, the two chips, or their replacements can not be exchanged against each other.
For the 1541, the EasyGate1541 would be the right replacement, and for the 1541-II, the EasyGate1541-II is now available, which I would like to introduce here in this article.
Actually, the differences between the two gate arrays are not that big. A few lines have been dropped because they are no longer needed due to a different stepper motor control and R/W amplifier for the read/write head and the clock generation has been integrated. Additionally a few gates have been integrated into the chip. That was it actually already.
At least the part for the 1541-II. There are still some functions for the 1571 integrated in this chip. But I did not deal with that in detail. Should a 1571 “fall” into my hands sometime, I would dedicate myself to the topic. But personally, the prices for used drives are too high for me, just to develop a chip that I personally don’t need.
Not much has changed in terms of design. This chip basically uses the same design, although minor changes were necessary due to the different PIN assignment.
However, a Xilinx XC9572XL in the 64PIN is now required. The gate array in the 1541-II needs a few more I/Os due to the added functions.
I had additionally added another LED for the 2MHz mode, should I ever get a 1571 and I then extend the firmware if necessary.
For the 1541-II this LED has no function, and could be simply omitted.
On my GitHub account you can find everything necessary to rebuild the EasyGate1541-II. Incl. the firmware and a manual for flashing: https://github.com/DL2DW/EasyGate1541-II