USB Memory Stick: an ideal memory device 1

Published:2011/8/8 2:17:00 Author:Amy From:SeekIC

By Harry Baggen

In no time at all, the USB Flash Drive or Memory Stick has become one of the most popular memory devices: small, robust, large capacity, no battery. Now that Elektor Electronics are offering a 128-MB USB Memory Stick as a welcome gift to new subscribers, it’s high time your favorite electronics magazine told you how it works.

Really useful, such a USB Flash drive. It will fit in your trouser pocket, does not eat batteries and holds lots and lots of computer data. Around for a number of years already, this memory device has become incredibly popular.

So what’s inside a Flash Drive and how does it work? Using our welcome gift to new (18-month) subscribers we’ll tell you, with a note that the description is applicable to other brands and types, too. The photograph shows that there’s preciously little inside a Flash drive. The main com­ponents are the Flash mem­ory (the big back slice at the top side) and the controller (with this type, at the under­side). There are also a couple of smaller SMD parts, a quartz crystal and an indica­tor LED signaling data access. A small slide switch is fitted at the side to provide write protection.

Two ICs

The block schematic structure of the two large ICs is shown in Figure 1. The Flash disk controller (here, an OTi-2168) is specially designed for this sort of application. It contains a fast RISC core that handles the complete communication with the Flash memory, enabling the computer connected to the Flash drive to ’think’ that a ordinary hard disk is con­nected to one of its USB ports. Furthermore, the OTi chip con­tains an integrated fast UB2.0 interface allowing the highest possible data speed of 480 Mbit/s to be achieved.



You may wonder why so much computing power is neces­sary. The answer is we’re not just looking at serial/parallel conversion but also at all the protocols that apply to access­ing the Flash memory. Com­plying with a protocol and thus establishing communica­tion with the Flash memory device over a number of I/O pins is radically different from driving a set of address and data pins on conventional RAM or EEPROM. The Flash memory is a 1024 Mbit (128 Mbyte) ’NAND’ type from Samsung driven via eight I/O lines. The controller issues commands for reading, writ­ing or erasing while also sup­plying the relevant addresses and data.

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