C8051F351 Silicon Laboratories Inc, C8051F351 Datasheet - Page 109

• Manufacturer Part Number: C8051F351
• Description: IC 8051 MCU 8K FLASH 28MLP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F35xr

Specifications of C8051F351

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 50MHz
• Connectivity: SMBus (2-Wire/I²C), SPI, UART/USART
• Peripherals: POR, PWM, Temp Sensor, WDT
• Number Of I /o: 17
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 768 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Data Converters: A/D 8x24b; D/A 2x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-VQFN Exposed Pad, 28-HVQFN, 28-SQFN, 28-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

13.
The C8051F350/1/2/3 family of devices incorporate a 2-byte prefetch engine. Because the access time of
the Flash memory is 40 ns, and the minimum instruction time is 20 ns, the prefetch engine is necessary for
full-speed code execution. Instructions are read from Flash memory two bytes at a time by the prefetch
engine, and given to the CIP-51 processor core to execute. When running linear code (code without any
jumps or branches), the prefetch engine allows instructions to be executed at full speed. When a code
branch occurs, the processor may be stalled for up to two clock cycles while the next set of code bytes is
retrieved from Flash memory. The FLRT bit (FLSCL.4) determines how many clock cycles are used to read
each set of two code bytes from Flash. When operating from a system clock of 25 MHz or less, the FLRT
bit should be set to ‘0’ so that the prefetch engine takes only one clock cycle for each read. When operat-
ing with a system clock of greater than 25 MHz (up to 50 MHz), the FLRT bit should be set to ‘1’, so that
each prefetch code read lasts for two clock cycles.
Bits 7-6: Unused. Read = 00b; Write = Don’t Care
Bit 5:
Bits 4-1: Unused. Read = 0000b; Write = Don’t Care
Bit 0:
Bit7
R
Prefetch Engine
PFEN: Prefetch Enable.
This bit enables the prefetch engine.
0: Prefetch engine is disabled.
1: Prefetch engine is enabled.
FLBWE: Flash Block Write Enable.
This bit allows block writes to Flash memory from software.
0: Each byte of a software Flash write is written individually.
1: Flash bytes are written in groups of two.
Figure 13.1. PFE0CN: Prefetch Engine Control Register
Bit6
R
PFEN
R/W
Bit5
Bit4
R
Rev. 0.4
Bit3
R
Bit2
R
C8051F350/1/2/3
Bit1
R
SFR Address: 0xE3
FLBWE
R/W
Bit0
00100000
Reset Value
109