EXPERIMENT D6: MEMORY CIRCUIT Related course: KEEE2232 (Digital Design) OBJECTIVES: To understand the structure of the simplest ROM, basic structure of Random Access Memory (RAM), structure and applications of Random Access Memory (RAM), theory, structure and applications of EPROM and the t he characteristics and applications applications of EEPROM EQUIPMENT: Module KL-33010, KL-33011 PREPARATIONS: Follow the demonstrator instructions throughout the experiment REFERENCE(S): Refer to the main references of KEEE2232 (Digital Design) TESTS: TEST 1: TEST 2: TEST 3: TEST 4: TEST 5:
Constructing Read Only Memory (ROM) with Diodes Constructing Random Access Memory (RAM) with D Flip-Flop Structure and applications of Random Access Memory (RAM) Erasable Programmable Programmable Read Only Memory (EPROM) Circuit Electronic EPROM (EEPROM) Circuit
TEST 1: Constructing Read Only Memory (ROM) with Diodes INTRODUCTION: Figure 1 shows the basic circuit of a simple ROM made up of diodes and a 3-8 line decoder. A0, A1 and A2 are input terminals. Incoming data are controlled by diodes. The 3-line address has 8 states and there are four data at the output. The output capacity is 8x4. The truth table for address input and data output are shown in Table 1.
Figure 1
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Table 1 Address input A2 A1 A0 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1
D3 0 0 0 1 1 1 0 0
Data output D2 D1 0 0 0 1 1 1 1 1 0 0 1 0 1 1 0 1
D0 1 1 1 1 0 0 0 1
If outputs O0-O3 pass through a 3-state gate, then it can be used in conjunction with other ROM, with an additional "Enable" terminal to control the other ROM. Figure 2 shows how four ROMs are used in parallel. The data terminals D0-D7 and Address Select A0-A7 are connected in series. When CS1=0 and CS2 - CS4 =1, data in ROM1 is selected. CS1 -CS4 only allow one data to be accessed at a time.
Figure 2 To allow selection of different ROMs, CS1 - CS4 passes through a 2-4 decoder. The input is controlled by A8, A9; as shown in Figure 3.
Figure 3 If A9A8 = "00", ROM1 is selected. If A9A8 = "01 ", ROM2 is selected. If A9A8 = "10 ", ROM3 is selected. If A9A8 = "11 ", ROM4 is selected. 8
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The capacity of each ROM is (2 )x8 (A7-A0=2 , D0-D7=8-bit), the total capacity is (2 )x8x4= 1kB.
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PROCEDURES: 1. 2. 3. 4. 5.
Insert connection clips according to Figure 4. Connect inputs D1, D2 to data switches SW0 and SW1 Record the output when D2, D1 =01 and when D2,D1 =10. If the power is cutoff and turned on again, will the outputs be the same? Construct a ROM that has the following outputs in Table 2 using diodes and 2-4 decoder.
Figure 4
A 0 0 1 1
B 0 1 0 1
Table 2 F3 F2 1 0 1 1 0 0 0 0
F1 0 0 1 0
F0 1 0 0 1
TEST 2: Constructing Random Access Memory (RAM) with D Flip-Flop 1. Block g of module KL-33010 is used for this experiment. 2. Connect E1, S1, D1 and D2 to Data Switch SW0-SW3 respectively. Connect outputs F1, F2 and F3 to Logic Indicators L1-L3. Refer to the input sequence in Table 3 and record all outputs.
Figure 5
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Table 3
QUESTIONS: 1. Which one of the following devices can be used as a memory? Flip-flop / Basic gate / NAND gate 2. How many flip-flops are required to construct a 3-bit memory? 2 / 3 / 4 3. What is equivalent to the ENABLE terminal when a D flip-flop is used as memory? Output Q / Input D / Input clock CK 4. DRAM is a: Write only memory / Read only memory / Read only memory
TEST 3: Structure and applications of Random Access Memory (RAM) 1. Insert connection clip according to Figure 6, Connect the + 12V and +5V power supply. 2. Connect inputs D4-D1 to DIP Switch 1; A3-A0 DIP Switch 2; ME to Pulse Switch SWA; WE to Data Switch SW0. Outputs are indicated by CR4-CR1. 3. Set SW0 (WE) to "0" for the "WRITE" task. Start from address 0000, input any. Activate SWA once (ME) to write the data into its assigned address. Repeat this process for all the addresses, ending with 1111. Record what was written into each address in Table 4 under the "WRITE" column. 4. Set SW0 (WE) to "1”or the "READ" task. Observe states of CR1-CR4 and record under the "READ" column in Table 4. 5. Disconnect “A:’ clip and SWA (ME), then turn off the main power switch for about 10 seconds and turn it on again. Are they still stored in the RAM? 6. Disconnect “B” clip. Repeat Step 5 to see if the data are still stored in the RAM.
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Figure 6 Table 4
EXERCISES: 1. Use the 7489 and 7447 RAM to construct a digital display that displays these numbers in sequence: 2-5-4-8-7-1-0-9. 2. Connect addresses A0-A2 of 7489 to a counter so that when A3=0, it will shift left and flash when A3=1. Use 7493 and 7489.
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QUESTIONS: 1. Which device stores data permanently? RAM / PROM / ROM 2. Which device will lose all data in case of power interruption? RAM / ROM / PROM 3. To avoid losing data due to power interruption, which of the following option is most viable? Rechargeable battery / Do not interrupt the power / Use only DC battery 4. Which terminal is responsible for selecting the action of the memory? POWER / ENABLE / GROUND 5. In which mode does the memory store data? READ and WRITE / READ / WRITE 6. Which memory has both the READ and WRITE function? RAM / ROM / Both 7. Chip select for RAM is: WR / RD / CE TEST 4: Erasable Programmable Read Only Memory (EPROM) Circuit During the process of program development, data stored in ROM have to be modified and edited quite often. Although PROMs (Programmable Read Only Memory) allow users to write-in data by themselves, it is an one-time only device and is a very inconvenient, uneconomical to use if several modifications are necessary. Figure 7 shows the general schematic of an EPROM.
Figure 7 The most obviously, and easily distinguishable mark on an EPROM is the quartz window on the top surface. On the inside, it is the Metal-Oxide semiconductor Field Effect Transistor (MOSFET) that sets EPROM apart from other memories. In a brand new EPROM, no bias exist at any of the MOSFETs so the MOSFETs are not conductive, outputs D0-D3 are at logic "1" initially. If logic "0" is required at a certain bit, an EPROM Writer must be used to apply a certain voltage (depend on EPROM specifications, typically 21V or 25V) to this particular bit, injecting electrons into the gate. Since the gates are covered with insulating materials, the electrons are trapped inside. The gates now become negatively charged, creating a path in the MOSFET and making it conductive, or logic "0". Exposure to ultraviolet light, through the quartz window, will erase data stored in the EPROM. The duration of exposure depends on the amount, or length of data stored. When the MOSFETs are exposed to ultraviolet light, the trapped electrons gains enough energy to escape the insulating material, thus making the MOSFET not conductive. QUESTIONS: 1. Which of these memories is erased by exposure to ultraviolet light? EPROM / RAM / PROM
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2. Which of this component can use as memory? Diode / Resistor / Capacitor 3. What's the major difference between ROM and EPROM? Voltage requirements / Pin assignments / Quartz window 4. Which of these memories is most suitable for mass production? ROM / PROM / EPROM 5. Which of these is most suitable for use in laboratories? ROM / PROM / EPROM 6. What are EPROMs made of? Fuse / FET / Bipolar transistor 7. What is used to write data into ICs? High temperature / High voltage / High frequency 8. Which memory will lose its data when power is interrupted? RAM / PROM / EPROM 9. Which is used for EPROM control signal? RD / WR / WR and RD 10. What can replace EPROM? EEPROM / PROM / ROM
TEST 5: Electronic EPROM (EEPROM) Circuit The only difference between EEPROM and EPORM is how they are erased, While EPROM is erased by exposure to ultraviolet light, and EEPROM is erased by voltage so it has no quartz window. Writing or EEPROM is accomplished by connecting a pin to a voltage higher than its supply voltage and erasure is done by selling all data to "HI" (Hi state), This characteristic enables EEPROMs to be erased address by address, whereas all addresses in EPROM will be erased when exposed to ultraviolet light. Therefore, EEPROM is more convenient to use than EPROM. EEPROM is very useful for storing tables or charts that are not accessed often and does not change too frequently. The 2864 EEPROM is used in this experiment. Its pin assignment and truth table are shown in Figures 8 and 9 respectively.
Figure 8 A0 – A12
I/O0 – I/O7 Vpp
Figure 9 Address Chip enable Output enable Input / Output Program voltage
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1. Complete the circuit shown in Figure 10. Connect Vcc to +5V. 2. Connect inputs D7-D0 to DIP Switch 1; A10-A8 to Ground and A7-A0 DIP Switch 2; Chip Enable (CE), Output Enable (OE) and Write Enable (WE) to data switches; F7F0 to logic indicators. 3. Record what was written into any 16 addresses in Table 5 under the "WRITE" column. Follow Figure 11 for Write process. 4. Observe and record the data under the "READ" column in Table 5. Follow Figure 12 for Read process. 5. Then turn off the main power switch for about 10 seconds and turn it on again. Are they still stored in the EEPROM?
Figure 10
Figure 11: controlled write cycle
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Figure 12: Read cycle
Address A7 – A0
Table 5 Write Data D7 – D0
Read Data D7 – D0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 QUESTION: 1. How is EEPROM erased? It can not be erased / With voltage / With ultraviolet light 2. For the EEPROM 2864, WE which voltage for the "READ" operation? +5V / 0V / 21 V 3. For the EEPROM 2864, Vpp must be connected to which voltage for the "WRITE" operation? +5V / 0V / 21V
END OF EXPERIMENT
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