µPAD Proto Base Manual 1773KB May 14 2015 09:31:12 AM

µPAD: Proto Base Manual
Last Updated May 13, 2015
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Table of Contents
WARNING: READ BEFORE PROCEDING! ...................................................................................................... 7
Overview ..................................................................................................................... Error! Bookmark not defined.
µPAD Base Connection .......................................................................................................................................... 8
Analog ..................................................................................................................................................................... 8
Amplifier Circuit .................................................................................................................................................. 8
Amplifier Calculations ..................................................................................................................................... 9
Analog/PORTB Selector(s) ................................................................................................................................. 10
Single ended vs. Differential ............................................................................................................................... 10
Single Ended Conversion Considerations ........................................................................................................... 10
PORTB ADC Pin Mapping ................................................................................................................................. 11
Xmega Digital Pins ............................................................................................................................................... 12
CPLD .................................................................................................................................................................... 15
CPLD/MCU Selectors ........................................................................................................................................ 16
Breadboard Area .................................................................................................................................................. 16
Keyboard Area ..................................................................................................................................................... 17
LCD Interface ....................................................................................................................................................... 17
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Figure 1: Board Top Un-Assembled
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Figure 2: Board Top Fully Assembled
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Figure 3: Bottom Board Fully Assembled
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Figure 4: µPAD Top
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Figure 5: µPAD Bottom
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WARNING: READ BEFORE PROCEDING!
1. It is possible to damage your µPAD irreparably through the use of poor software. PORTB 0 and
PORTB 1 pins serve special functions. PORTB 0 is the input for the precision 2.5V analog
reference, and PORTB 1 is the Circuit GND reference input for differential analog measurements.
If you set the direction register for PORTB pins 0 or 1 you risk
destroying your board! Always use caution when using PORTB of the µPAD’s
Xmega!!!
2. Use caution when connecting and disconnecting µPAD from the µPAD Proto Base J2 pictured in
Figure 1. This connector can be sheared off the PCB if handled roughly.
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µPAD Base Connection
The µPAD Proto Base connects directly to the µPAD through connector J2 which can be seen in Figure 1.
All electrical signals from the µPAD to the µPAD Proto Base pass through this connection.
Analog
The µPAD Proto Base has an external analog front end circuit which allows the µPAD to read signals
between 0 to 5V, when using the µPAD’s precision 2.5V external reference.
Amplifier Circuit
The following circuit displayed in Figure 4 is the analog front end for ADC input 4 of PORTB.
Figure 4: Analog Front End
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Amplifier Calculations
The following calculations assumes an ideal op-amp
Assumption:
Vi+ = ViGiven:
ADC4 = VIN
AFE4 = VOUT
Equations:
𝑉𝑖+ = 𝑉𝑖𝑛 ∗
𝑅9
500
𝑉𝑖𝑛
= 𝑉𝑖𝑛 ∗
=
𝑅11 + 𝑅9
1500
3
𝑉𝑜𝑢𝑡 – 𝑉𝑖+ 𝑉𝑖+ − 0
=
𝑅5
𝑅7
𝑉𝑜𝑢𝑡 – 𝑉𝑖+ 𝑉𝑖+ − 0
=
500
1000
𝑉𝑜𝑢𝑡 – 𝑉𝑖+ 𝑉𝑖+ − 0
=
1
2
𝑉𝑜𝑢𝑡 =
3𝑉𝑖+
2
With a substitution of Vi+
𝑉𝑜𝑢𝑡 =
3 𝑉𝑖𝑛
∗
2 3
The end relationship is then…
𝑉𝑜𝑢𝑡 =
𝑉𝑖𝑛
2
Note: The amplifier circuit(s) utilizes 1% resistors throughout
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Analog/PORTB Selector(s)
The Analog/PORTB selector(s) can be found in the upper right corner of Figure 3. This group of 4
selectors is used to control whether PORTB pins 4-7 are connected to their respective analog front end
circuits, or their respective PORTB breakout connections in J9 pictured in Figure 2. Each pin 4-7 can be
individually configured per its respective selector. In Figure 3 all pins, 4-7, are connected to their
respective analog front end circuit.
Single ended vs. Differential
Analog to Digital Converters are devices that convert a voltages to numeric values that a processor can
use for calculations etc. There are two kinds of ADCs differential and single ended. Voltage inherently is
a differential measurement. It is the electric potential difference of two nodes, which in this context are
referred to as the positive and negative inputs. In the case off single ended converters the negative input
of the ADC is internally connected to circuit GND. Differential converters however have a dedicated
negative input in addition to a positive one. Differential converters are particularly useful when
measuring voltages independent or circuit GND.
The µPAD’s Xmega is capable of taking both single ended and differential measurements. However
differential type measurements yield more accurate results. For this reason the µPAD was designed with
a solder jumper SJ1, visible in Figure 5, to measure circuit GND directly with the Xmega pin PORTB 1.
If you wish to take differential measurements you should solder the pads of SJ1 together. The µPAD will
need to be removed from the µPAD Proto Base to solder this jumper. Single ended conversions can be
taken with or without soldering the SJ1 jumper.
Single Ended Conversion Considerations
The µPAD’s Xmega is inaccurate at measuring circuit GND internally, which is why the differential
interface is more accurate. That being said if single ended measurements are to be performed signed
conversions are recommended again for accuracy. When using singed vs. unsigned measurements the top
bit of the ADC conversion is used to indicate the measured voltage as positive or negative. Simply put
signed mode measurements, though more accurate, have half the resolution of unsigned measurements.
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PORTB ADC Pin Mapping
Table 1 below displays the pin mapping used for various types of conversions with the Xmega ADC. It is
important to note that differential measurements without gain and differential measurements with gain have
positive and negative inputs flipped. In particular measurements taken with gain will be return negative
values. This physical limitation can be easily adjusted for in software.
Table 1: ADC Pin Mapping
PORTB
Pin
Single Ended
Pin Function
DIFF Pin
Function
DIFF GAIN Pin
Function
0
AREF
AREF
AREF
1
-
ADC1 NEG
(GND REF )
ADC1 POS (GND
REF)
2
-
-
-
3
-
-
-
4
-
ADC4 POS
ADC4 NEG
5
-
ADC5 POS
ADC5 NEG
6
-
ADC6 POS
ADC6 NEG
7
-
ADC7 POS
ADC7 NEG
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Xmega Digital Pins
The µPAD has several Digital pins serving various purposes. The following table describes these pins
and their functions. Reference Figure 2 for the reference designators.
Table 2: Digital Pin Mapping
Reference
Designator
Pin
Number
Signal
Name
Function
J5
0
PORTF 7
GPIO
J5
1
PORTF 6
GPIO
J5
2
PORTF 5
GPIO
J5
3
PORTF 4
GPIO
J5
4
PORTF 3
GPIO
J5
5
PORTF 2
GPIO
J5
6
PORTF 1
GPIO
J5
7
PORTF 0
GPIO
J6
0
ADDR 82
EBI ADDR
J6
1
ADDR 92
EBI ADDR
J6
2
ADDR 102
EBI ADDR
J6
3
ADDR 112
EBI ADDR
J6
4
ADDR 122
EBI ADDR
J6
5
ADDR 132
EBI ADDR
J6
6
ADDR 142
EBI ADDR
J6
7
ADDR 152
EBI ADDR
J7
0
GND
Power
J7
1
WE
GPIO,EBI CTRL
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J7
2
RE
GPIO,EBI CTRL
J7
3
ALE
GPIO,EBI CTRL
J7
4
CS0
GPIO,EBI CTRL
J7
5
CS1
GPIO,EBI CTRL
J7
6
CS2
GPIO,EBI CTRL
J7
7
CS3
GPIO,EBI CTRL
J9
0
3.3V
Power
J9
1
PORTB 2
GPIO, DAC
J9
2
PORTB 3
GPIO, DAC
J9
3
PORTB 41
GPIO
J9
4
PORTB 51
GPIO
J9
5
PORTB 61
GPIO
J9
6
PORTB 71
GPIO
J9
7
GND
Power
J10
0
PORTE 0
GPIO
J10
1
PORTE 1
GPIO
J10
2
PORTE 2
GPIO
J10
3
PORTE 3
GPIO
J10
4
PORTE 4
GPIO
J10
5
PORTE 5
GPIO
J10
6
PORTE 6
GPIO
J10
7
PORTE 7
GPIO
J11
0
ADDR 0
GPIO,EBI ADDR
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J11
1
ADDR 1
GPIO,EBI ADDR
J11
2
ADDR 2
GPIO,EBI ADDR
J11
3
ADDR 3
GPIO,EBI ADDR
J11
4
ADDR 4
GPIO,EBI ADDR
J11
5
ADDR 5
GPIO,EBI ADDR
J11
6
ADDR 6
GPIO,EBI ADDR
J11
7
ADDR 7
GPIO,EBI ADDR
J12
0
DATA 0
GPIO,EBI DATA
J12
1
DATA 1
GPIO,EBI DATA
J12
2
DATA 2
GPIO,EBI DATA
J12
3
DATA 3
GPIO,EBI DATA
J12
4
DATA 4
GPIO,EBI DATA
J12
5
DATA 5
GPIO,EBI DATA
J12
6
DATA 6
GPIO,EBI DATA
J12
7
DATA 7
GPIO,EBI DATA
1) These pins must be selected as digital pins using the
PORTB/Analog selector(s)
2) These are latched address signals.
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CPLD
The µPAD Proto Board contains a 44 pin PLCC socket (U2) intended for a MAX 3000 series CPLD.
This socket can be viewed in Figure 2. Through this device logic such as memory mapping can be
implemented.
Table 3: CPLD GPIO Signal Mapping
Reference
Designator
Header
pin
CPLD
Pin
J8
1
24
J8
2
26
J8
3
29
J8
4
34
J8
5
37
J8
6
39
J8
7
GCLK1
J8
8
5
J13
1
27
J13
2
28
J13
3
31
J13
4
33
J13
5
41
J13
6
40
J13
7
GCLK2
J13
8
4
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CPLD/MCU Selectors
J3 is used to bridge significant signals of the Xmega’s External Bus Interface (EBI) over to the CPLD for
performing address decoding.
Table 4: MCU/CPLD Selector Mapping
Signal Name
CPLD Pin
ADDR 15
8
ADDR 14
6
ADDR 13
9
ADDR 12
11
CS3
12
CS2
14
CS1
16
CS0
19
ALE
18
RE
21
WE
20
Breadboard Area
The breadboard area of the µPAD Proto Base is designed for use with DIP and other through whole
components. The breadboard area is displayed at the bottom of Figure 2. Vertical dashes in the silk
screen denote shorts between holes.
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Keyboard Area
The µPAD Proto Base was designed to connect to a keypad breakout board via a 2x5 pin cable. This
cable connects at J23 labeled “Keypad Input”, and is displayed in Figure 2. In order to read from the
keypad either rows or columns will need to be pulled high or low. J20 is used to house a 10 pin SIP
resistor as well as a 10 pin header for wire wrapping. The label for J20 is most easily found in Figure 1,
but the header soldered to it can be viewed in Figure 3. J21 and J22 are used to connect keypad signals to
a SIP resistor located at J20. The keypad signals are directly connected to J22. The reference designator
and the signal names therein are viewable in Figure 2. J21 pins, as indicated by horizontal dashes, are
shorted horizontally with the pins in J20 (best viewed in Figure 1). Jumpers can be used with J22 and J21
to connect keypad signals to a SIP resistor.
LCD Interface
The µPAD has dedicated mounts and electrical connections for a character LCD. The signal pins of the
LCD are wire wrap accessible via J29. Each of the LCD signals are labeled. J29 is just visible below the
LCD in Figure 2.
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