Marking Scheme
Lab 3

Pre-Lab

marks were assigned for the following answers:

- (1.) a schematic & parts placement diagram
- (1.) charge pumps increase or invert the voltage, the MAX232 has two charge pumps
- (2.) one handshaking lines false is low; on datalines 1 is low
- (5.) i = CdV/dt
- (6.) x10 probes reduce the capactive loading on circuit being measured from approximately 30+20=50pF to 12pF

Lab Report

marks were assigned for:

RS-232
- output impedance measures about 700ohm, not spec'ed
- input impedance measures about 7k & spec is 3k to 7k
- slew rate measured <30v/us (spec)
- current = CdV/dt ~= 5mA
- maximum frequency ~ 50kHz (20 kHz spec)

RS-422

- maximum bit rate >500 kHz
- RS-422 data rate is much greater than RS-232
- slew rate limits RS-323 rate
- RS-232 slew rate rate is limited "To reduce crosstalk between interchange circuits"
- RS-422 uses differential signaling & twisted pair to reduce crosstalk