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MaximIntegrated 17-3
MAX31782 User’s Guide
Revision 0; 8/11
The data byte portion of the 10-bit shift register is interfaced directly to the ICDB parallel register . The ICDB register
functions as the holding data register for both transmit and receive operations . On the falling edge of TCK in the Update-
DR state, the outgoing data is loaded from the ICDB parallel register to the debug shift register and the incoming shift
register data is latched in the ICDB parallel register .
17.1BackgroundModeOperation
When the instruction register is loaded with the Debug instruction (IR[2:0] = 010b), the host can communicate with the
MAX31782 in a background mode using TAP DR-Scan sequences without disturbing CPU operation . Note, however,
that JTAG in-system programming also requires use of the 10-bit debug shift register and, if enabled (JTAG_SPE = 1,
PSS[1:0] = 0), takes precedence over background mode communication . When operating in background mode, the
status bits are always cleared to 00b (non-debug), which indicates that the MAX31782 is ready to receive background
mode commands .
The host can perform the following operations from background mode:
• read/write internal breakpoint registers (BP0–BP5)
• read/write internal in-circuit debug registers (ICDC, ICDF, ICDA, ICDD)
• monitor to determine when a breakpoint match has occurred
• directly invoke debug mode
shows the background mode commands supported by the MAX31782 . Encodings not listed in this table are
not supported in background mode and are treated as no operations .
Figure 17-2. 10-Bit Word Format
Table17-1.StatusBits
Table17-2.BackgroundModeCommands
s[1:0]
STATUS/CONDITION
00
Non-Debug.
Default condition, background mode, or debug engine inactive .
01
DebugIdle.
Debug engine is ready to receive data from the host (command, data) .
10
DebugBusy.
Debug engine is busy without valid data (i .e ., ROM code execution, trace operations) .
11
DebugValid.
Debug engine is busy with valid data .
OPCODE
COMMAND
OPERATION
0000–0000
No Operation
Nooperation.
Default state for debug shift register .
0000–0001
Read ICDC
ReadcontroldatafromtheICDC.
The contents of the ICDC register is loaded into the debug
shift register through the ICDB register for host read . This command requires one follow-on trans-
fer cycle .
0000–0010
Read ICDF
ReadflagsfromtheICDF.
The contents of the ICDF register (1 byte) are loaded into the debug
shift register through the ICDB register for host read . This command requires one follow-on trans-
fer cycle .
TDI
TDO
9
0
9
0
X
X
s0
s1
HOST COMMAND/DATA INPUT
MAX31782 DATA OUTPUT
STATUS
MAX31782