6.5.10 I/O Short Address Location Register (SIM_ISALH and SIM_ISALL)
The I/O Short Address Location registers are used to specify the memory referenced via the I/O short
address mode. The I/O short address mode allows the instruction to specify the lower six bits of address;
the upper address bits are not directly controllable. This register set allows limited control of the full
address, as shown in Figure 6-14.
Note:
If this register is set to something other than the top of memory (EOnCE register space) and the EX bit
in the OMR is set to 1, the JTAG port cannot access the on-chip EOnCE registers, and debug functions
will be affected.
Instruction Portion
“Hard Coded” Address Portion
6 Bits from I/O Short Address Mode Instruction
16 Bits from SIM_ISALL Register
2 bits from SIM_ISALH Register
Full 24-Bit for Short I/O Address
Figure 6-14 I/O Short Address Determination
With this register set, an interrupt driver can set the SIM_ISALL register pair to point to its peripheral
registers and then use the I/O Short addressing mode to reference them. The ISR should restore this register
to its previous contents prior to returning from interrupt.
Note:
Note:
The default value of this register set points to the EOnCE registers.
The pipeline delay between setting this register set and using short I/O addressing with the new value
is three cycles.
Base + $D
Read
15
1
14
1
13
1
12
1
11
1
10
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
0
ISAL[23:22]
Write
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
RESET
Figure 6-15 I/O Short Address Location High Register (SIM_ISALH)
6.5.10.1 Input/Output Short Address Low (ISAL[23:22])—Bit 1–0
This field represents the upper two address bits of the “hard coded” I/O short address.
56F8367 Technical Data, Rev. 9
126
Freescale Semiconductor
Preliminary
FREESCALE [ Freescale ]
