WMS7204

Publication Release Date: January 2003

- 17 -

Revision 1.0

7.8.5 Reading Tap Registers and NVMEM Locations

The contents of the tap register for any channel or any NVMEM location can be read back through the

SDO pin. When a command is sent, the data is clocked out on the falling edge of the clock. Since

daisy-chain operation requires data from one command to be clocked out when the next command

arrives, any read command must be followed by another command to get the correct data on the SDO

pin.

TABLE 9 – READING THE TAP REGISTERS

Inst.

No.

Command

Name:

Command Byte

Data Byte 1

Data Byte 2

Comment

4

Read

NVMEM

1 0 1 0 A3 A2 A1 A0

x x x x x x x x

x x x x x x x x

Read the

value of the

selected

NVMEM

location

2

Read Tap

Register

1 1 0 0 x x A1 A0

x x x x x x x x

x x x x x x x x

Read the

value of the

selected

tap register

1

NOP to

Read

Register

0 0 0 0 x x x x

x x x x x x x D8

D7 D6 D5 D4 D3 D2 D1 D0

Output data

to SDO pin

To read the contents of either the tap register or a NVMEM location, the following sequence must be

followed.

1. Send the desired read command (#2 or #4) to select the register to read

2. Send another command such as NOP and read the SDO pin on the falling edge of the clock.

The other command could be any command, but to make sure that the chip does not change

anything, send either another Read command or a NOP command (#1).