I started developing my own JTAG program for my particular needs( my MIPS CPU)
It works OK for  IDCODE and IMPCODE instructions. In other words my program 
works well 
for those instructions that does not need any input data ( no need to change 
bits in EJTAG 
registers).

But it does not seem to work well for those instructions that needs input data.
For example for EJTAG Control Register.
As an example I want to halt the CPU ,so I must write
EjtagBrk bit( 12 bit  of EJTAG Control Register)
 into EJTAG Control Register.
Then  I should read DM bit( 3 bit of  EJTAG Control Register).
and if it is halted successfully, that bit must be set ( by CPU) to 1.

So I 
send CONTROL instruction that selects EJTAG Control register

But how shall I send the data into EJTAG Control Register?
I have a procedure that READs data from JTAG data register but not sure how to 
WRITE data 
into the JTAG data register.

And must I send CONTROL instruction both before writing data and before reading 
the results  or 
jast before writing data?

Thanks for help

        

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