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4.2.2. C
C
RYSTAL
HOICE
The operating crystal frequency has been chosen to support the fastest operation with the fastest serial operating speeds.
The value of the crystal is 18.432MHz.
The following table shows the baud rates and Baud Rate Register (BRR) setting required for each communication rate using
the above default operating speed. It also confirms the resultant baud rate and the bit error rate that can be expected.
SMR
0
Setting:
Comm.
BRR
Actual
Baud
setting
Rate
110
Invalid
Invalid
300
Invalid
Invalid
1200
Invalid
Invalid
2400
239
2400
4800
119
4800
9600
59
9600
19200 29
19200
38400 14
38400
57600 9
57600
115200 4
115200
230400* 2
192000
460800* 0
576000
* Note: The device used to convert the RS232 serial information to logic signals for the microcontroller is limited to
120kBaud. The rates above this level can only be utilised if the user provides direct logic level communications.
The user may replace the HC49/U surface mounted AT cut crystal with another of similar type within the operating frequency
of the microcontroller device. Please refer to the hardware manual for the microcontroller for the valid operating range.
Alternatively the user may fit an oscillator module – or provide an external clock source. When providing an oscillator module
or external source it is highly recommended that the load capacitors for the AT crystal are removed from the PCB. These are
physically placed within the PCB outline of the oscillator module for easy location and to ensure they are removed when
using this option.
When changing the crystal frequency the pre-loaded debugging monitor will not function. In this situation the user is
responsible for providing code to evaluate the device away from the default operating speed.
4.2.3. R
EMOVABLE COMPONENT INFORMATION
This information is provided to allow the replacement of components removed from the board as described in section 4.2.2.
Component
Load Resistor (X2)
Load Resistor (X3)
Load capacitors (X2)
Load capacitors (X3)
Care must be taken not to damage the tracking around these components. Only use soldering equipment designed for
surface mount assembly and rework.
4.3. SPI EEPROM
The board has been tested with an Atmel AT25040N-10SA-2.7 SPI EEPROM device (Not supplied).
The device should be connected to P30, P31, P32 and P67 using 0R links on R15, R16, R17 and R21. Alternative
connections are available, refer to section 5.3 for more information.
Do not fit the CAN transceiver if the SPI device is fitted while using the settings above.
Baud Rate Register Settings for Serial Communication Rates
1
ERR
BRR
Actual
(%)
setting
Rate
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
119
1200
0.00
59
2400
0.00
29
4800
0.00
14
9600
0.00
7
18000
0.00
3
36000
0.00
2
48000
0.00
0
144000
-16.67
Invalid
Invalid
25.00
Invalid
Invalid
T
4-2 C
ABLE
RYSTAL
.
Cct. Ref
Value
R8
1MΩ
R7
1MΩ
C2,C3
12pF
C4,C5
15pF
T
4-3: R
ABLE
EMOVABLE
2
ERR
BRR
Actual
(%)
setting
Rate
Invalid
Invalid
Invalid
Invalid
119
300
0.00
29
1200
0.00
14
2400
0.00
7
4500
0.00
3
9000
-6.25
1
18000
-6.25
Invalid
Invalid
-16.67
Invalid
Invalid
25.00
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
F
RS232
REQUENCIES FOR
COMMUNICATION
Rating
0805 1%
Welwyn WCR Series
0805 1%
Welwyn WCR Series
0603 10% 25V
AVX 0603 3 A 150 KAT
0603 10% 25V
AVX 0603 3 A 150 KAT
C
I
OMPONENT
NFORMATION
3
ERR
BRR
Actual
(%)
setting
Rate
Invalid
81
110
0.00
29
300
0.00
7
1125
0.00
3
2250
-6.25
1
4500
-6.25
Invalid
Invalid
-6.25
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Manufacturer
ERR
(%)
-0.22
0.00
-6.25
-6.25
-6.25
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
Invalid
7
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