Quiz 4 Flashcards
To study for Quiz 4, Thursday May 8
What is the difference between asynchronous and synchronous clocking?
Synchronous - synchronized by external clock
Asynchronous - synchronized by special signals along the transmission medium.
What are some advantages and disadvantages of synchronous clocking?
Advantages: Lower overhead => greater throughput.
Disadvantages: Slightly more complex; Hardware is more expensive.
What are some advantages and disadvantages of asynchronous clocking?
Advantages:
- Simple - doesn’t require synchronization of both communication sides
- Cheap - requires less hardware; well-suited for applications where messages are generated at irregular intervals (e.g. data entry from the keyboard) and the speed depends on different applications.
Disadvantages:
* Large relative overhead - a high proportion of the transmitted bits are uniquely for control purposes and thus carry no useful information
What can affect the performance of an asynchronous system?
A bad clock. Standard used is quartz-crystal oscillator due to precision of timing.
Extra information: Frequency of resonance once rock is trimmed accurately keeps time.
Asynchronous can only transfer ___ number of ___.
fixed, bits
The start bit in an asynchronously-timed clock ….
doesn’t carry any information
JTAG stands for
Joint Test Action Group
JTAG can have ___ or ___ pins
4, 5
What are the different pins that can come on JTAG? Which one(s) is/are optional?
TDI, TDO, TCK, TMS, TRST
TRST is optional
TDI
Test Data In; goes into shift register
TDO
Test Data Out; leaves shift register
TCK
Test clock; connected to input of shift register
TMS
Test Mode Select; connected to output of shift register
In a JTAG, the device under test is wired through I/O lines into the _______
shift register
The device under test in a JTAG is usually a
chip on a board we want to test
SPI
Serial Peripheral Interface
Is SPI synchronous or asynchronous?
synchronous
What is the SPI’s data rate?
data rate is variable
What is an alternate name/acronym for SPI?
SSI - Synchronous Serial Interface
TRST
Test Reset; optional connector on JTAG
MOSI
master output, slave input: logic signal on SPI bus
MISO
master input, slave output: logic signal on SPI bus
What are some possible slave devices for SPI?
clock/calendar, potentiometer, memory
How many master / slave devices can work with SPI?
One master device, one or more slave devices.
I2C
Inter-Integrated Circuit
What is the I2C?
Multimaster serial single-ended computer bus
What is the max number of devices for I2C?
128
SDA
Serial data
SCL
Serial clock line
Acknowledge logic signals on I2C
1: Master wants to send info to slave
0: Master wants to receive info from slave
Slave does not initiate communication
In which direction can data flow on I2C?
From master to slave or slave to master
Address always comes from ____ in I2C exchange
master
How fast is I2C?
100 to 400kb/s
How many bits of data does I2C support?
8
The vast majority of RS-232 setups are
asynchronous
Voltage of RS-232
Old systems used +/- 12V, now use 0V for low, 5V for high
Types of parity
Even, odd, mark, space, none
Even parity
If already even number of 1’s - 0
If odd number of 1’s - 1
Odd parity
If even number of 1’s - 1
If odd number of 1’s - 0
Mark parity
Always 1
Space parity
Always 0
Why is parity bit useful?
Good for error-checking bits
RS-232 Data Signals
“Space” Logic 0 (HIGH) = +12
“Mark” Logic 1 (LOW) = -12
Data size for RS-232
5, 6, 7, or 8 bits
5, 6, 7 use a bit old; modern systems typically use 8
Baud vs bits/sec
baud rate is a measure of how many times per second a signal changes (or could change).
bps is simply the number of bits transmitted per second.
What are the two connector options for RS-232?
9pin and 25pin
DTE
data terminal equipment
DCE
data communications equipment
RS-232C Control Signals
RTS, CTS, DCD, DSR, DTR, RI, +/-12V
RTS
request to send: DTE tells DCE to receive data
CTS
clear to send: DCE says ready to receive
DCD
data carrier detect: DCE detects a carrier
DSR
data set ready: DCE tells DTE it is on and ready
DTR
data terminal ready: DTE tells DCE it is on; if inactive all other signals ignored
RI
ring indicator: DCE tells DTE a ring has occurred
+12V
Logic 1 (RS-232C Control Signal)
-12V
Logic 0 (RS-232C Control Signal)
