IDT EJTAG System
EJTAG Test Access Port
79RC32438 User Reference Manual
20 - 64
November 4, 2002
Notes
The contents of the Data register are not aligned but hold data as it is seen on a data bus for an external
memory system. Thus the bytes are positioned in the Data register based on access size, address, and
endianess. The bytes not accessed for a processor access write are undefined, and the bytes not accessed
for a processor access read can be written with any value by the probe shifting the value into the Data
register.
Table 20.46 shows the byte positioning for a 32-bit processor (MIPS32/64 = 0), in which case the two
LSBs of the Address register are used. Byte 0 refers to bits 7:0, byte 1 refers to bits 15:8, byte 2 refers to
bits 23:16, and byte 3 refers to bits 31:24, independent of endianess.
Address Register (TAP Instruction ADDRESS or ALL)
Compliance Level
: Required with EJTAG TAP feature.
The read-only Address register provides the address for a processor access. The width of the register
corresponds to the size of the physical address in the processor implementation (from 32 to 64 bits). The
specific length is determined by shifting through the Address register, because the length is not indicated
elsewhere. The value read in the register is valid if a processor access is pending, otherwise the value is
undefined. The two or three LSBs of the register are used with the Psz field from the EJTAG Control
register to indicate the size and data position of the pending processor access transfer. These bits are not
taken directly from the address referenced by the load/store.
Figure 20.31 shows the format of the Address register and Table 20.47 describes the Address register
field.
Fields
Description
Read/
Write
Reset
State
Compli-
ance
Name
Bit
Data
MSB:0
Data used by processor access.
R/W
Undefined
Required
Table 20.45 Data Register Field Description
Psz
from
ECR
Size
Address[1:
0]
Little
Endian
Big Endian
3
2
1
0
3
2
1
0
0
Byte
00
2
01
2
10
2
11
2
1
Halfword
00
2
10
2
2
Word
00
2
3
Triple
00
2
01
2
Reserved
n.a.
n.a.
Table 20.46 Data Register Contents for 32-bit Processors