Renesas EDK3687 Technical Information download pdf (Page 9)

4.2.2. CRYSTAL CHOICE

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.

Baud Rate Register Settings for Serial Communication Rates

SMR

Setting:

0 1 2 3

Comm.

Baud

BRR

setting

Actual

Rate

ERR

(%)

BRR

setting

Actual

Rate

ERR

(%)

BRR

setting

Actual

Rate

ERR

(%)

BRR

setting

Actual

Rate

ERR

(%)

110

Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid 81 110 -0.22

300

Invalid Invalid Invalid Invalid Invalid Invalid 119 300 0.00 29 300 0.00

1200

Invalid Invalid Invalid 119 1200 0.00 29 1200 0.00 7 1125 -6.25

2400

239 2400 0.00 59 2400 0.00 14 2400 0.00 3 2250 -6.25

4800

119 4800 0.00 29 4800 0.00 7 4500 -6.25 1 4500 -6.25

9600

59 9600 0.00 14 9600 0.00 3 9000 -6.25 Invalid Invalid Invalid

19200

29 19200 0.00 7 18000 -6.25 1 18000 -6.25 Invalid Invalid Invalid

38400

14 38400 0.00 3 36000 -6.25 Invalid Invalid Invalid Invalid Invalid Invalid

57600

9 57600 0.00 2 48000 -16.67 Invalid Invalid Invalid Invalid Invalid Invalid

115200

4 115200 0.00 0 144000 25.00 Invalid Invalid Invalid Invalid Invalid Invalid

230400*

2 192000 -16.67 Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid

460800*

0 576000 25.00 Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid Invalid

TABLE 4-2 CRYSTAL FREQUENCIES FOR RS232 COMMUNICATION

* 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. REMOVABLE COMPONENT INFORMATION.

This information is provided to allow the replacement of components removed from the board as described in section 4.2.2.

Component Cct. Ref Value Rating Manufacturer

Load Resistor (X2) R8

1MΩ

0805 1% Welwyn WCR Series

Load Resistor (X3) R7

1MΩ

0805 1% Welwyn WCR Series

Load capacitors (X2) C2,C3 12pF 0603 10% 25V AVX 0603 3 A 150 KAT

Load capacitors (X3) C4,C5 15pF 0603 10% 25V AVX 0603 3 A 150 KAT

TABLE 4-3: REMOVABLE COMPONENT INFORMATION

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.

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