
System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
6-6
Freescale Semiconductor
occupying the external bus. Internal bus arbitration is selected by clearing SIUMCR[EARB] (see
6.1.2.2
Address Decoding for External Accesses
During an external master access, the USIU compares the external address with the internal address block
to determine if MPC561/MPC563 operation is required. Since only 24 of the 32 internal address bits are
available on the external bus, the USIU assigns zeros to the most significant address bits (ADDR[0:7]).
The address compare sequence can be summarized as follows:
Normal external access. If EMCR[CONT] is cleared, the address is compared to the internal
— MPC561/MPC563 special register external access. If EMCR[CONT] is set by the previous
external master access, the address is compared to the MPC561/MPC563 special address
— Memory controller external access. If the first two comparisons do not match, the internal
memory controller determines whether the address matches an address assigned to one of the
regions. If it finds a match, the memory controller generates the appropriate chip select and
attribute accordingly
When trying to fetch an MPC561/MPC563 special register from an external master, the address might be
aliased to one of the external devices on the external bus. If this device is selected by the
MPC561/MPC563 internal memory controller, this aliasing does not occur since the chip select is
disabled. If the device has its own address decoding or is being selected by external logic, this case is
resolved.
NOTE
This section does not address slave accesses to internal resources. For
internal resources, the accesses compare against ADDR[8:9] = ISB[1:2].
ISB0 must be cleared.
6.1.3
USIU General-Purpose I/O
The USIU provides 64 general-purpose I/O (SGPIO) pins (See
Table 6-2). The SGPIO pins are
multiplexed with the address and data pins. In single-chip mode, where communicating with external
devices is not required, all 64 SGPIO pins can be used. In multiple-chip mode, only eight SGPIO pins are
available. Another configuration allows the use of the address bus for instruction show cycles while the
data bus is dedicated to SGPIO functionality. The functionality of these pins is assigned by the single-chip
SGPIO pins are grouped as follows:
Six groups of eight pins each, whose direction is set uniformly for the whole group
16 single pins whose direction is set separately for each pin
Table 6-2 describes the SGPIO signals, and all available configurations. The SGPIO registers are