1University of California at BerkeleyCollege of EngineeringDepartment of Electrical Engineering and Computer ScienceCS150 J. Warzynek and N. WeaverFall 2000 Revisions by R. Fearing, X. Zhang, B. Choi, and N. ZhouCS150 Project Check Point #1Wire-Wrap, SRAM, and FIFO design.1 ObjectivesFor this lab, you will:1. Learn to use Wire-Wrap.2. Gain more practice in digital design3. Learn some strategies to test circuits4. Wire an SRAM to the Xilinx on your Design Demonstration Board and test it.2 Prelab Fllowing the directions in Section 3, use Wire-Wrap to connect a W24512AK, an 64K x 8 SRAMto the Xilinx chip on your Design Demonstration Board. Use the pinouts in Figure 2 and Wrap-ID fromPage 5.Design the FIFO and SRAM access logic for the circuit described in Section 53 Wire-WrapWire-Wrap is a prototype construction technique where 30-gauge wire (``Wire-Wrap wire'') istwisted around a square post to make aconnection. These connections are physically strong, reliable,electrically sound, and quickly made.A Wire-Wrap tool consists of three parts:• A central hexagonal rod with a wire stripper in the center (the little black notch).• The wrapping end: a black circular rod with a hole in the center and an off-center hole leading to aside slot.• The unwrapping end: a shorter circular rod with a hole in the center.Wrapping EndUnwrapping EndWire StripperHole forWireHole forPinSlot forWireWrapping End Unwrapping EndHole forWireHole forPinSlot forWireWire StripperFigure1 Wire-Wrap tool (not to scale)2To make a Wire-Wrap connection1. Plan the route of your wire. Leave little slack, perhaps a half inch. Wires shouldlie flat against the board.2. Cut the wire~2.5 inches longer than the route you chose.3. Strip an inch of insulation off each end of the wire using the Wire-Wrap tool'sstripper: thread the wire through the circular hole in the hexagonal handle, push itinto the stripper's notch, and pull.4. Insert a stripped end of the wire into the off-center hole in the end of the wrappingend of the tool. The wire should be visible in the slot on the side, although itshould not hang out of this slot.5. Put the wrapping end of the tool on the pin to be connected. The pin should fiteasily in the center hole.6. Gently, without pushing down or lifting up, twist the tool clockwise about twelverevolutions. This should wrap a few turns of insulated wire around the bottom,followed by the stripped wire. There should be a single layer of wire, with nospaces between turns.If you make a mistake connecting a wire, remove it completely and start again. Place the unwrappingend of the tool on the pin and turn counter-clockwise. The wire should slide off. An unwrapped wireshould not be re-wrapped.Use differently colored wire to group signals. For example, make the data lines in this lab green, theaddress lines orange, and the control signals red.It is easy to forget that when you Wire-Wrap, the chip's pins appear as the mirror image of the usualpinout diagram. The best solution is to use a Wrap-ID, something that fits over the Wire-Wrap pins withthe (correctly mirrored) pinout written on it. Such a Wrap-ID is printed on Page 5---cut it out, and carefullypush it down on the pins before you start wiring your W24512AK.A few hints on wire wrapping:• Always use Wrap-IDs. We will always provide you with Wrap-IDs, but if you ever need to wire wrapsomething and you don't have one, make one.• Be neat. Although it is difficult to produce perfectly pristine connections, you should keep the wires asflat and as neet as possible. Messy wirewrap is much harder to debug, and is less reliable.• Check for wire fragments. It is quite possible to have a little piece of wire fall down and short out twopins. Look carefully at the wires to make sure this does not happen.• Inspect each connection after you make it, to insure it is to the right place and that the connection issolid. If you have a digital multimeter(If you don't, inexpensive ones are available at Radio Shack.You probably should buy one, they are good things to have.), use it to check each connection after youmake it.4 SRAMsAn SRAM (Static RAM) is a standard form of digital storage. It is generally faster, simpler, andmore expensive then DRAM (Dynamic RAM).SRAMs are nice when one needs to store a moderate but notexcessive amount of data, and needs to retrieve it quickly.The W24512AK you use is a high speed SRAM. It takes only 15nanoseconds for an address toproduce output data, and comes in a standard DIP package.3Their electrical interface is simple:• eight data pins, for input and output• address input pins. The~W24512AK, 216 = 65536-byte part, has 16 address pins.• an active-low and an active high chip enable inputs (CE1 and CE2), and an active-low output enableinput (OE)• an active-low write enable (WE).• power (VCC) and ground (GND) pinsFor this projectCE1 should be tied ground physically since we only need one chip enable signal. CE2should be high to enable the chip for read and write operations. To read the chip, lower the OE input, thechip will respond by driving the data I/O to the content of the memory at the location specified by theaddress input, change the address and the output will change. To write to the chip, lower the WE input thedata at the address will change to reflect the data I/O.5 testing the SRAM and the FIFOThere are generally two ways to test a memory, by producing specific patterns, or by a brute forceapproach. A set of specific patterns would test each wire a line at a time, to insure the output is correct.Brute force simply checks all possible values. For this lab, we will use brute force approach, as it is easierto implement. We will provide 2 bit files U:/cs150/Chk_pt1/SRAM test`(slow).bit and a …(fast).bit whichtests the SRAM, but you should also build your own version.The slow one runs at 128KHz and the fast one runs at 8MHz. Both circuits test writing andreading from all addresses of memory from 0000 to 7FFF. (note this does not test the A15 so you have totake extra care not to wire it wrong (and yes I did that for a reason)). The upper bits of the address isdisplayed on the number LEDs. If you wire-wrapped correctly, the circuit will continuously run through thememory and never stop. Other wise it will stop and the top 2 bits on the bar LED will light up.Figure2 W24512AK Pinout (top view) and pins on the XilinxAdditional wirings: (CE2 14), (CE1 GND), (NC GND)A1 9A2
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