PLC
Programmable Controllers - device for industrial sequential operation management such as assembly, packing etc.
PLC Basic Symbols
Transmission Gates
- X and C=0 — 0
- X and C=1 — X
- X or C=0 — X
- X or C=1 — 1
- X ExOR C=0 — X
- X ExOR C=1 — NOT X
Compliment of a number
- compliment of 123 = 1000 - 123 = 877
- compliment of 2411 = 10,000 - 2411 = 7589
- To subtract a number, add the compliment and remove the first digit
Two’s Compliment
- Inverse digits and add 1
- eg. twos compliment of 1010 = 0101 +1 = 0110
Size of register and size of compliment number
- size of register determines compliment length
- eg. 4 bit: compliment of 0110 = 1010
- eg. 8 bit: compliment of 0110 = 1111 1010
Flags
- Status Register
- Z = result zero (1), result not zero (0)
- N = result negative (1), result not negative (0)
- C = Carry Generated (1), carry not generated (0)
- V = Overflow (1), no overflow (0)
- Carry = if result is too large to fit in the same number of binary numbers as original numbers (work out using decimal and convert back!)
- Overflow = If the sign bit of the both operands are the same and the sign bit of the result is different
Two forms of encoding digital info
NRZ and NRZI
NRZ
- No return to zero.
- simplist
- difficult to keep clock when sending out long strings of 0 or 1
NRZI
- No return to zero inverted
- Transmission rule:
- If data bit =1, change level
- If data bit = 0, dont change
- Advantage: ensures 1 is transmitted safely
Successive Approxiations - Converting Analogue to digital
- Analogue input applied to computer
- clock used to generate binary numbers
- D to A converter translated numbers to analogue voltage and sends to computer
- If Vclock > Vin, gate closes and binary number stops increasing
Latching
A circuit, which one energise,maintains that state untl another input is recieved
Machine Leel
Digital code to translate assembly langage to binary
Assembly Language
Primitive language that an operater uses
Types of RAM
- SRAM, once the input is given, the content will remain until changed by a subsequent valid input.
- The data storage device in the DRAM bit cell is a capacitor. When a logic 1 is written to the bit cell, it charges up the capacitor until the voltage across it is also a logic 1. As the charge in the bit cell tends to drop, the memory is continuously refreshed for keeping its contents. This gives it its name of dynamic RAM.
e differences between a microprocessor and a microcontroller
- A microprocessor (CPU)
- complete processor contained in one or a few LSI circuits, used to build a computer.
- A microcontroller
- LSI circuit containing a microprocessor, memory and I/O system.
Difference between memory location and data register
- A memory location is a part of the whole memory area provided by the computer. It is for storing a program instruction, or data.
- A register in a computer is a storage, and is designed to be accessed by the processor at an even faster speed than memory.
Status Register
It scans and reflects the status of the arithmetic and logic after each instruction has been executed. Flags used.
