13. JTAG > JTAG Register Access
112
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
•
DR[16:0] = 17b’0
Note
: Bit 0 is shifted first, and bit 66 is shifted last.
3.
Move to the “Run-test idle” state and loop in this state for a minimum of 20 TCK cycles.
4.
Move to the “Shift-DR” state again and shift the Ready bit and Error bit through JTAG_TDO (see
).
•
First bit shifted out is the Ready bit.
•
Second bit shifted out is the Error bit.
•
Verify that the Ready bit is at logic high and the Error bit is at logic low.
Note
: To prevent corruption, the DR register must be loaded as described in step 2 while
shifting out through JTAG_TDO for observation.
5.
Go back to step 2 to perform another write.
13.6.3
Read Access to Registers from JTAG Interface
Complete the following steps to read a device register through the JTAG Interface:
1.
Move to the TAP controller “Shift-IR” state and program the instruction register with IRAC
instruction by writing into Instruction Register bits with 0xFFFF_FFFF_FFFF_FFFD.
This step is optional if the instruction register is already programmed during the write cycle.
2.
Move to the “Shift-DR” state and shift the R/W = 0 and the address[9:0] serially in the TDI pin. To
prevent corruption of unused bits, the full DR bits have to be written as follows (see also
):
•
DR[66:62] = 5b’0
•
DR[61:52] = ADDR[9:0]
1
•
DR[51] = R/W
•
DR[50:19] = DATA[31:0]
•
DR[18:17] = 2b’0
•
DR[16:0] = 17b’0
Note
: Bit 0 is shifted first, and bit 66 is shifted last.
3.
Move to the “Run-test idle” state and loop in this state for a minimum of 20 TCK cycles.
4.
Move to the “Shift-DR” state again and shift the Ready bit, Error bit, and data[31:0] out through
JTAG_TDO (see
).
•
First bit shifted out is the Ready bit.
•
Second bit shifted out is the Error bit.
1. Note that the address here is the DWORD address, not the byte address. Take the byte address and remove the 2 LSBs, >>2.