C80 51 F 53 x/5 2x
Rev. 0.4
7
5.2. System Clock Sources
The C8051F530A device installed on the target board features a calibrated programmable internal oscillator that is
enabled as the system clock source on reset. After reset, the internal oscillator operates at a frequency of
191.4 kHz (±0.5%) by default but may be configured by software to operate at other frequencies. Therefore, in
many applications, an external oscillator is not required. However, if you wish to operate the C8051F530A device
at a frequency not available with the internal oscillator, an external crystal may be used. Refer to the C8051F52x/
52xA/53x/53xA data sheet for more information on configuring the system clock source.
The target board is designed to facilitate the installation of external crystals. Install the crystals at the pads marked
Y1 or Y2. Install a 10 M
resistor at R17 or R22, and install capacitors at C29 and C30 or C34 and C35 using
values appropriate for the crystals selected. Headers J9, J10, J11, and J12 connect the external crystal pins to the
general purpose I/O headers (J1 and J2). If the external crystal is in use, these headers should not be populated.
Refer to the C8051F52x/52xA/53x/53xA data sheet for more information on the use of external oscillators.
5.3. Switches and LEDs
Four switches are provided on the target board.
Switch RESET_A is connected to the RESET pin of the C8051F530A A-Side (U2).
Switch RESET_B is connected to the RESET pin of the C8051F530A B-Side (U1).
Pressing RESET_A or RESET_B puts the attached device into its hardware-reset state.
Switches P1.4_A and P1.4_B are connected to the C8051F530A parts (U1 and U2) general purpose I/O (GPIO)
pins through headers. Pressing P1.4_A or P1.4_B generates a logic low signal on the port pin of the respective
microcontroller.
Remove the shorting block from the header to disconnect P1.4_A or P1.4_B from the port pins. The port pin
signals are also routed to pins on the J1 and J2 I/O connectors. See Table 2 for the port pins and headers
corresponding to each switch.
Four LEDs are also provided on the target board. The red LED labeled PWR is used to indicate a power
connection to the target board. The green LEDs labeled D1 and D2 are connected to the C8051F530A's GPIO pins
through headers. Remove the shorting blocks from the headers to disconnect the LEDs from the port pins. The port
pin signals are also routed to pins on the J1 and J2 I/O connectors. The red LED labeled USB ACTIVE is used to
indicate that the CP2102 USB-to-UART bridge is properly connected to a PC and is ready for communication. See
Table 2 for the port pins and headers corresponding to each LED.
A potentiometer (R32) is provided on the target board. Header J8 connects the potentiometer to +5 V, and header
J6 connects the potentiometer to the P1.2_A pin of the U2 A-Side C8051F530A microcontroller.
Table 2. Target Board I/O Descriptions
Description
I/O
Header
Reset_A
U2-Reset
none
Reset_B
U1-Reset
none
P1.4_A
U2-P1.4
HDR4[3–4]
P1.4_B
U1-P1.4
HDR3[3–4]
Green LED D2
U2-P1.3
HDR4[1–2]
Green LED D1
U1-P1.3
HDR3[1–2]
Red LED D3
PWR
none
Red LED D4
USB ACTIVE
none
Potentiometer R32
U2-P1.2
J6, J8
