JM20330 board without M/S jumper compatible w/ Dreamshell

[Gillbert]

I just like to share a solution for a problem, maybe someone is in the same boat.

I had bought some of these IDE-SATA adapters from eBay years ago but unfortunately they don't have a master/slave select jumper so that it was impossible to use them along with Dreamcast/Dreamshell, as everybody knows that the device must be set as slave mode in order to work.



It's a Jmicrom JM20330 chipset based board. I was pretty sure this chipset was indeed compatible with DC since I have used other different boards with same chipset and they work fine, so I decide to investigate a little and compared the boards and I then was able to understand how to enable the M/S jumper selection from JM chip.

Note that there is a mark in the board called"SW1" which initially I thought could be a M/S select but it has nothing to do with mode selection:



I found that the pin 33 is the one responsible for M/S select mode. The incompatible board had this pin soldered to ground (low state) so that it only operated in master mode. In order to enable slave mode this pin have to be assigned to an high state (3,3V).





I lifted pin 33 from board (it was a bit tricky job...), added a 1K resistor and wired it to a 3,3V point (I used the out pin of a 3V3 voltage regulator). Now the slave mode was successfully enabled. Later I completed the mod adding a jumper board in order to choose between M/S modes:



Here's a diagram for illustrating the mod:



Cheers!

[boxcutter]

good info.

acording to the datasheet the chip has an internal pulldown resistor, so they had no need to ground the pin anyway!