C8051F50x-F51x
15.4.3. System Clock
1. If operating from an external crystal, be advised that crystal performance is susceptible to electrical
interference and is sensitive to layout and to changes in temperature. If the system is operating in an
electrically noisy environment, use the internal oscillator or use an external CMOS clock.
2. If operating from the external oscillator, switch to the internal oscillator during Flash write or erase
operations. The external oscillator can continue to run, and the CPU can switch back to the external
oscillator after the Flash operation has completed.
Additional Flash recommendations and example code can be found in ”AN201: Writing to Flash from Firm-
ware" available from the Silicon Laboratories web site.
SFR Definition 15.1. PSCTL: Program Store R/W Control
Bit
7
6
5
4
3
2
1
0
PSEE
PSWE
Name
Type
Reset
R
0
R
0
R
0
R
0
R
0
R
0
R/W
0
R/W
0
SFR Address = 0x8F; SFR Page = 0x00
Bit
7:2
1
Name
Unused Read = 000000b, Write = don’t care.
PSEE Program Store Erase Enable.
Function
Setting this bit (in combination with PSWE) allows an entire page of Flash program
memory to be erased. If this bit is logic 1 and Flash writes are enabled (PSWE is logic
1), a write to Flash memory using the MOVX instruction will erase the entire page that
contains the location addressed by the MOVX instruction. The value of the data byte
written does not matter.
0: Flash program memory erasure disabled.
1: Flash program memory erasure enabled.
0
PSWE Program Store Write Enable.
Setting this bit allows writing a byte of data to the Flash program memory using the
MOVX write instruction. The Flash location should be erased before writing data.
0: Writes to Flash program memory disabled.
1: Writes to Flash program memory enabled; the MOVX write instruction targets Flash
memory.
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Rev. 1.1
SILICON [ SILICON ]
