Register Descriptions
The upper four bits of the GPIOB register can function as GPIO, [A23:20], or as additional clock output
signals. GPIO has priority and is enabled/disabled via the GPIOB_PER. If GPIOB[7:4] are programmed
to operate as peripheral outputs, then the choice between [A23:20] and additional clock outputs is done
here in the CLKOSR. The default state is for the peripheral function of GPIOB[7:4] to be programmed as
[A23:20]. This can be changed by altering [A23:20] as shown in Figure 6-9.
Base + $A
Read
15
0
14
0
13
0
12
0
11
0
10
0
9
A23
0
8
A22
0
7
A21
0
6
A20
0
5
4
3
0
2
CLKOSEL
0
1
0
0
0
CLK
DIS
Write
0
0
0
0
0
0
1
0
RESET
Figure 6-9 CLKO Select Register (SIM_CLKOSR)
6.5.7.1
Reserved—Bits 15–10
This bit field is reserved or not implemented. It is read as 0 and cannot be modified by writing.
6.5.7.2
Alternate GPIOB Peripheral Function for A23 (A23)—Bit 9
•
•
0 = Peripheral output function of GPIOB7 is defined to be A23
1 = Peripheral output function of GPIOB7 is defined to be the oscillator_clock (MSTR_OSC in Figure 3-4)
6.5.7.3
Alternate GPIOB Peripheral Function for A22 (A22)—Bit 8
•
•
0 = Peripheral output function of GPIOB6 is defined to be A22
1 = Peripheral output function of GPIOB6 is defined to be SYS_CLK2
6.5.7.4
Alternate GPIOB Peripheral Function for A21 (A21)—Bit 7
•
•
0 = Peripheral output function of GPIOB5 is defined to be A21
1 = Peripheral output function of GPIOB5 is defined to be SYS_CLK
6.5.7.5
Alternate GPIOB Peripheral Function fpr A20 (A20)—Bit 6
•
•
0 = Peripheral output function of GPIOB4 is defined to be A20
1 = Peripheral output function of GPIOB4 is defined to be the prescaler_clock (FREF in Figure 3-4)
6.5.7.6
Clockout Disable (CLKDIS)—Bit 5
•
•
0 = CLKOUT output is enabled and will output the signal indicated by CLKOSEL
1 = CLKOUT is tri-stated
6.5.7.7
CLockout Select (CLKOSEL)—Bits 4–0
Selects clock to be muxed out on the CLKO pin.
•
•
•
•
00000 = SYS_CLK (from OCCS - DEFAULT)
00001 = Reserved for factory test—56800E clock
00010 = Reserved for factory test—XRAM clock
00011 = Reserved for factory test—PFLASH odd clock
56F8367 Technical Data, Rev. 9
Freescale Semiconductor
Preliminary
119
FREESCALE [ Freescale ]
