Section 2 - RS 232

Question 1

RS 232 voltage levels

Answer 1

+5 to +15V = 0
-5 to -15V = 1

Question 2

RS 232 characteristics

Answer 2

unbalanced, unterminated, single ended, point to point (one sender, one receiver), max speed = ~20 kB/s @ 50ft, max distance = 2.4kB/s @ 300ft

Question 3

RS 422 characteristics

Answer 3

Differential signal, terminated, balanced, terminating resistors @ end of bus, can be connected to up to 10 devices, connected devices are only receivers, -2 to -6 = 1 and 2 to 6v = 0, max speed = 10 MB/s @40ft, max distance = 100kB/s @ 4000ft

Question 4

RS 485 characteristics

Answer 4

Differential signal, most common in industry, terminated, balanced, terminating resistors @ end of bus, can connect 32 devices, devices can transmit and receive, -1.5 to -6 = 1 and 1.5 to 6v = 0, tri-state output (0, 1 or no signal), max speed = 10 MB/s @40ft, max distance = 100kB/s @ 4000ft

Question 5

Longitudinal redundancy checking (LRC)

Answer 5

a parity is sent with each bit to verify if it is correct or wrong but only works with an odd number of errors and not even

Question 6

Logical checksums

Answer 6

The data is added together and the result is sent as a data byte at the end (only LSB)

Question 7

Cyclic redundancy checking (CRC)

Answer 7

A block of data is sent and a code is sent (typically 16 bits). Good chance of catching any errors (99.9%+). One of the most popular methods although its calculation is difficult.