Registers

Notes

• This is Carpinelli Chapter 7
• We have discussed registers before
  • n data input lines
  • n data output lines
  • enable and a clock.
• We can easily consider building one of these with a set of d flip-flops.
  • 
  • The 74273 is an example
  • No enable, but a clear.
• A shift register is fairly common
  • While we have not looked at it in depth, shifting is useful
  • Division/multiplication by 2
  • And, as we will see, for other things.
• I very useful register is single data input register.
  • See the 74595 (we will look at this later)
  • There is one data input bit.
  • There is a clock and a shift control input.
  • The data will be shifted across the register.
  • 
  • This is useful if I have a single line for data.
  • I transmit it in serial to the register, then read it in parallel.
  • I can improve this by adding a "second register"
  • This is loaded from the first on a clock signal
  • 
  • The top register is a load "buffer"
  • Put the data in this by shifting
  • When that is done, load the "storage" register with load.
• The 74595
  • Inputs include
    • A oe output enable not line
      • This controls the output from the data register.
      • A single line driving 8 tri-state devices.
    • A rclk or register clock
      • This controls the transfer of data from the buffer to the register
      • Simply the clock for all of the register flip-flops
    • A crclr line that clears the buffer bits.
    • A srclk line, the clock for the buffer
    • A ser line, or input data.
  • Outputs include
    • 8 (Q_A - Q_H) output bits from the register
    • 1 (Q_H') output of the value of the last buffer bit
      • This allows chaining these chips to allow for more than 8 bits.
  • Remember flip-flops can be built with a clear and a set line.
  • 
• Ben Eater builds an eeprom programmer with the 74595
  • here
  • It uses and Arduino nano
    • This has a limited number of digital outputs.
    • guide
    • I know that this says 22 outputs, but some of these are not usable.
    • This device has a usb port
      • It can be programmed in c++
      • And interact with a computer.
  • He wants to program an eeprom chip that has
    • 8 data lines
    • 10 address lines
    • Along with a Write Enable and a Chip Enable
    • data sheet
• We have been building shift left (or double) registers.
• Can you build a shift right (or half) register?
• Could you build a sign fill shift right register?
• We could build a shift left/right/load register
  • It takes n data bits
  • A line for shift/load
  • A shift direction line
  • A clock line
  • and possibly a fill bit.
  • Use n 4 input multiplexors
  • 
• The digital file