The release of the 2.7 hardware contained only minor changes, and the addition of a part - GT20SL16S1Y. This is labelled on the schematic as U20.
After scouring the internet for hours with various combinations of the part number, I have been anable to find any reference to a device that even remotely fits the description. In fact, the existance of six pin serial memory devices is quite uncommon - most are 8 pin.
The best I could find was from a Russian forum, where the writer of the post claimed it was for “font”. A google translation error?
I eventually decided to crack my DSO open and see if there was a typo in the part number… and much to my surprise, there is no U20! That is, there is a place for it on the PCB, but no part fitted.
My personal best guess it was a pre-specified part that never made it into production. The DSO203 v2.7 was designed for it, but it was left off because it didn’t physically exist.
If any of the designers read this, could they please clarify what U20 is, and what it was meant to be used for?
Having poked about the schematic a bit, and being a long time circuit designer myself, there are many (what I would term) stupid mistakes. It seems as though the non-existant U20 (GT20SL16S1Y) could be used as either additional memory, or as a replacement for the current memory. As I said in my original post, I can’t find any reference to a part number that is even vaguely similar (which is a serial memory device).
It would not make sense that U20 would replace U13, as most SPI serial xRAM chips are 8 pins, and not 6. In fact 6 pin xRAM chips are really hard to find.
As you point out, it is wired to the same SPI bus but enabled with ZKCS. If it were to be a replacement, it should be wired to EECS so that no firmware change would be needed to access it.
I already thinking a hardware mod, using ZKCS but with an 8 pin xRAM chip soldered on top of U13… it would need a firmware change to access it though…
Oh! What is the other thread you refer to. I have not been able to find it…
If there are stupid mistakes in the schematic, that U20 is hardly one of them. I think it is simply a some obscure part that is not widely available outside the local markets in China. I wouldn’t worry about it, because it hardly seems significant.
If someone wants to expand the memory, I would suggest replacing the flash chip with a microSD card. It would be easy enough to patch the BIOS to replace the access routines (like AlterBIOS does).
OK, the word stupid is a bit harsh. Apologies if I offended. They are mistakes I would have made in my early days too.
I am not really worried about U20 missing, but I was more interested in what purpose the designer had in mind, and why he/she chose that particular (chinese only?) device.
U13 is very low capacity, and replacement with another device would seem prudent (a true uSD for example). However, I wonder if U20 was meant to be a SRAM/FRAM device (not flash/EEPROM/etc) to increase the amount of RAM available from the minimal amount in the CPU (and FPGA), and hence allow true RAM access without worrying about write cycle longevivity?
There are (few) applications where more RAM is required, and it would be nice to not worry about endurance.
