Figure 1. Crystal Configuration
Portable video recorder
Memory card readers
Legacy conversion devices
20 × PLL
12-pF capacitor values assumes a trace capacitance
of 3 pF per side on a four-layer FR4 PCA
The CLKOUT pin, which can be three-stated and inverted using
internal control bits, outputs the 50% duty cycle 8051 clock, at
the selected 8051 clock frequency: 48 MHz, 24 MHz, or 12 MHz.
FX2LP contains two standard 8051 USARTs, addressed through
Special Function Register (SFR) bits. The USART interface pins
are available on separate I/O pins, and are not multiplexed with
UART0 and UART1 can operate using an internal clock at
230 KBaud with no more than 1% baud rate error. 230 KBaud
operation is achieved by an internally derived clock source that
generates overflow pulses at the appropriate time. The internal
clock adjusts for the 8051 clock rate (48 MHz, 24 MHz, and
12 MHz) such that it always presents the correct frequency for
230 KBaud operation.
3.2.3 Special Function Registers
Certain 8051 SFR addresses are populated to provide fast
access to critical FX2LP functions. These SFR additions are
enhanced 8051 registers. The two SFR rows that end with “0”
and “8” contain bit addressable registers. The four I/O ports A to
D use the SFR addresses used in the standard 8051 for ports 0
to 3, which are not implemented in FX2LP. Because of the faster
and more efficient SFR addressing, the FX2LP I/O ports are not
addressable in external RAM space (using the MOVX
The “Reference Designs” section of the
for more information.
3. Functional Overview
3.1 USB Signaling Speed
FX2LP operates at two of the three rates defined in the USB
Specification Revision 2.0, dated April 27, 2000:
Full speed, with a signaling bit rate of 12 Mbps
High speed, with a signaling bit rate of 480 Mbps.
FX2LP does not support the low speed signaling mode of
3.2 8051 Microprocessor
The 8051 microprocessor embedded in the FX2LP family has
256 bytes of register RAM, an expanded interrupt system, three
timer/counters, and two USARTs.
3.2.1 8051 Clock Frequency
FX2LP has an on-chip oscillator circuit that uses an external
24 MHz (±100 ppm) crystal with the following characteristics:
FX2LP supports the I
C bus as a master only at 100/400 KHz.
SCL and SDA pins have open-drain outputs and hysteresis
inputs. These signals must be pulled up to 3.3V, even if no I
device is connected.
12 pF (5% tolerance) load capacitors
All packages, 8-bit or 16-bit “FIFO” bidirectional data bus, multi-
plexed on I/O ports B and D. 128-pin package: adds 16-bit
output-only 8051 address bus, 8-bit bidirectional data bus.
An on-chip PLL multiplies the 24 MHz oscillator up to 480 MHz,
as required by the transceiver/PHY and internal counters divide
it down for use as the 8051 clock. The default 8051 clock
frequency is 12 MHz. The clock frequency of the 8051 can be
changed by the 8051 through the CPUCS register, dynamically.
1. 115 KBaud operation is also possible by programming the 8051 SMOD0 or SMOD1 bits to a “1” for UART0, UART1, or both respectively.
Document #: 38-08032 Rev. *M
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