Chapter 10. Memory, CPLDs, and FPGAs

10.1 Read-Only Memory A read-only memory (ROM) is a combinational circuit with n inputs and b outputs. (Fig. 10-1) A ROM stores the truth table of an n-input, b-output combinational logic function. A decoder implemented by ROM (Table 10-1, Fig. 10-2) ROM is a kind of non-volatile memory. A 4x4 multiplier implemented by ROM. (Table 10-3) Internal structure of A diode ROM. (Fig. 10-5) A ROM using two-dimensional decoding. (Fig. 10-7) Internal structure of a MOS transistor ROM (Fig. 10-8)

Commercial ROM types (Table 10-5) Mask ROM Programmable Read-Only Memory (PROM) Erasable Programmable Read-Only Memory (EPROM) Floating gate technology (Fig. 10-10) Programmed by applying a HIGH voltage on the non-floating gate, and erased by exposing it to ultra-violet light. Electrically Erasable Programmable Read-Only Memory (EEPROM) Flash ROM Some standard ROMs (Fig. 10-11) Output Enable (OE) to control tri-state outputs. Chip-Select (CS) to enable the ROM chip. Address decoding of ROM applications (Fig. 10-12)

ROM for low power application (Fig. 10-13) ROM timing (Fig. 10-14) tAA: Access time from address. tACS: Access time from chip select. tOE: Output Enable time. The propagation delay from OE and CS both asserted until the output drivers have left the Hi-Z state. tOZ: Output-Disable Time tOH: Output-Hold time

10.2 Read/Write Memory RAM (Random Access Memory): most popular read/write memory. The time it takes to read/write a bit of memory is independent of the bit’s location. Static RAM (SRAM) Dynamic RAM (DRAM) SRAM and DRAM are both volatile. Ferroelectric RAM A kind of non-volatile RAMs.

10.3 Static RAM Basic structure of an SRAM (Fig. 10-19) Read operation Write operation Internal structure of an SRAM RAM cell (Fig. 10-20) A 8x4 SRAM SRAM timing Read timing (Fig. 10-22) tAA: Access time from address tACS: Access time from chip select tOE: Output-Enable time tOZ: Output-Disable time tOH: Output-Hold time

Standard static RAMs (Fig. 10-24) Write timing (Fig. 10-23) tAS: Address setup time before write tAH: Address hold time after write tCSW: Chip-select setup before end of write tWP: Write pulse width tDS: Data setup time before end of write tDH: Data hold time after end of write WE-controlled write versus CS-controlled write (Fig. 10-23) Standard static RAMs (Fig. 10-24) Asynchronous SRAM and Synchronous SRAM

10.4 Dynamic RAM DRAM structure and operation A DRAM cell (Fig. 10-31) Write operation Setting the word line to 1. To store a 1, a HIGH voltage is placed on the bit line, which charges the capacitor through the “on” transistor. To store a 0, a LOW voltage is placed on the bit line, which discharges the capacitor through the “on” transistor. Read operation The bit line is first precharged to a voltage halfway between HIGH and LOW. The word line is set HIGH so that the precharged bit line is pulled slightly higher or slightly lower. A sense amplifier detects this small change and recovers a 1 or 0 accordingly.

DRAM timing Synchronous DRAM Reading a DRAM cell destroy the original voltage stored on the capacitor, the DRAM cell must be written back the original data after reading. DRAM refresh (Fig. 10-32) Internal structure of a 64Kx1 DRAM (Fig. 10-33) Multiplexed address inputs RAS_L: Row address strobe to store the higher order bits of the address into the row-address register. CAS_L: Column address strobe to store the lower order bits of the address into the column-address register. Row latches: the latches used to store data input/output from the memory array. DRAM timing RAS-only refresh-cycle timing (Fig. 10-34) Read cycle (Fig. 10-35) Write cycle (Fig. 10-36) Synchronous DRAM

10.5 Complex Programmable Logic Devices 10.6 Field-Programmable Gate Arrays (FPGA) Xilinx XC4000 FPGA family Configurable logic block (CLB) (Fig. 10-44) Configurable interconnect structure (Fig. 10-46) CLB and wiring details (Fig. 10-47)