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UM0404
The central processing unit (CPU)
Note:
Register SYSCON cannot be changed after execution of the EINIT instruction.
The function of bit XPER-SHARE, VISIBLE, WRCFG, BYTDIS, ROMEN and ROMS1 is
described in more detail in
Section 8.2: External bus modes on page 183
System clock output enable (CLKEN)
The system clock output function is enabled by setting bit CLKEN in register SYSCON to '1'.
If enabled, port pin P3.15 takes on its alternate function as CLKOUT output pin. The clock
output is a 50 % duty cycle clock whose frequency equals the CPU operating frequency
(f
OUT
= f
CPU
). In case XCLKOUTDIV register is used, the f
OUT
can be equal to the
PWDCFG
Power Down Mode Configuration Control
‘0’: Power Down Mode can only be entered during PWRDN instruction
execution if NMI pin is low, otherwise the instruction has no effect. To exit
Power Down Mode, an external reset must occur by asserting the RSTIN pin.
‘1’: Power Down Mode can only be entered during PWRDN instruction
execution if all enabled fast external interrupt EXxIN pins are in their inactive
level. Exiting this mode can be done by asserting one enabled EXxIN pin (or
alternate source see
Section 5.6.1: Fast external interrupts on page 115
) or
with external reset.
CSCFG
Chip Select Configuration Control
‘0’: Latched Chip Select lines, CSx changes 1 TCL after rising edge of ALE.
‘1’: Unlatched Chip Select lines, CSx changes with rising edge of ALE.
WRCFG
Write Configuration Control
(Inverted copy of WRC bit of RP0H)
‘0’: Pins WR and BHE retain their normal function.
‘1’: Pin WR acts as WRL, pin BHE acts as WRH.
CLKEN
System Clock Output Enable
(CLKOUT)
‘0’: CLKOUT disabled, pin may be used for general purpose I/O.
‘1’: CLKOUT enabled, pin outputs the system clock signal or a prescaled
value of system clock according to XCLKOUTDIV register setting.
BYTDIS
Disable/Enable Control for Pin BHE
(Set according to data bus width)
‘0’: Pin BHE enabled.
‘1’: Pin BHE disabled, pin may be used for general purpose I/O.
ROMEN
Internal Memory Enable
(Set according to pin EA during reset)
‘0’: Internal memory disabled: accesses to the IFlash Memory area use the
external bus.
‘1’: Internal memory enabled.
SGTDIS
Segmentation Disable/Enable Control
‘0’: Segmentation enabled (CSP is saved/restored during interrupt entry/exit).
‘1’: Segmentation disabled (Only IP is saved/restored).
ROMS1
Internal Memory Mapping
‘0’: Internal memory area mapped to segment 0 (00’0000h...00’7FFFh).
‘1’: Internal memory area mapped to segment 1 (01’0000h...01’7FFFh).
STKSZ
System Stack Size
Selects the size of the system stack (in the IRAM) from 32 to 1024 words.
Bit
Function