MOTOROLA
Chapter 24. READI Module
24-15
Programming Model
Table 24-11. RWA Read/Write Access Bit Descriptions
RCPU
Bits
Nexus
Bits
Name
Description
0
79
SC
The start complete (SC) field is set when a read or write access is initiated. The device
will clear the SC bit once the read or write access completes. During a block access,
if the SC bit is reset, the access will terminate.
0 Access complete
1 Start access
1:25
78:54
RWAD
Read/write address (RWAD) bits are used to identify the address of internal
memory-mapped resources to be accessed, or the lowest address (i.e., lowest
unsigned value) for a block move (CNT > 0). The address range for a block move is
from RWAD to RWAD + CNT.
NOTE: The RWD field of the UDI register is shared with the WD field of the RWA
register.
26
53
RW
The read/write (RW) field can be configured to allow selection of a read or a write
access.
0 Read access
1 Write access
27:28
52:51
SZ
The word size (SZ) field can be configured to allow 32-bit, 16-bit, or 8-bit read/write
accesses. If the field is configured to one of the reserved states, its action reverts to
that of the default state.
00 32-bit
01 16-bit
10 8-bit
11 Reserved
29:60
50:19
WD
Write data (WD) bits contain the data to be written. For a read access, the data stored
is a don’t care.
61:62
18:17
PRV
The Privilege Attribute Field can be configured to select different read/write access
attributes.
00 User Data
01 User Instruction
10 Supervisor Data
11 Supervisor Instruction
63
16
MAP
The Map Select Field can be configured to allow access to multiple memory maps.
The primary processor memory map (MAP equal to 0b0) is designated as the default.
The secondary memory map (MAP equal to 0b1) can be set to select the MPC500
special purpose registers.
0 Primary memory map
1 Secondary memory map (PPC Special Purpose Registers)
64:79
15:0
CNT
The Access Count Field can be configured to indicate the number of accesses of word
size (defined in SZ field). The CNT value is used to increment the specified address
in the RWAD field for block read/write accesses.
For a single read/write access, the CNT value should equal to 0x0000. A 64-Kbyte
block read/write access can be performed by configuring the CNT bits as 0xFFFF. If a
user wants to terminate a block read or write access which has not completed, the
CNT bits should be reset.