
Rev:  1.10  8/2000
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com
25/34
1998, Giga Semconductor, Inc.
Preliminary
.
GS881Z18/36T-11/100/80/66
Boundary Scan Register
Boundary Scan Register is a collection of flip flops that can be preset by the logic level found on the RAM’s input or I/O pins. The 
flip flops are then daisy chained together so the levels found can be shifted serially out of the JTAG Port’s TDO pin.  The Boundary 
Scan Register also  includes a number of place holder flip flops (always set to a logic 1). The relationship between the device pins 
and the bits in the Boundary Scan Register is described in the Scan Order Table following. The Boundary Scan Register, under the 
control of the TAP Controller, is loaded with the contents of the RAMs I/O ring when the controller is in Capture-DR state and then 
is placed between the TDI and TDO pins when the controller is moved to Shift-DR state. Two TAP instructions can be used to 
activate the Boundary Scan Register. 
 JTAG TAP Block Diagram
Identification (ID) Register
The ID Register is a 32-bit register that is loaded with a device and vendor specific 32-bit code when the controller is put in 
Capture-DR state with the IDCODE command loaded in the Instruction Register. The code is loaded from a 32-bit on-chip ROM. 
It describes various attributes of the RAM as indicated below. The register is then placed between the TDI and TDO pins when the 
controller is moved into Shift-DR state. Bit 0 in the register is the LSB and the first to reach TDO when shifting begins.
ID Register Contents
Tap Controller Instruction Set
Overview
There are two classes of instructions defined in the Standard 1149.1-1990; the standard (Public) instructions, and device specific 
Die
Revision
Code
Not Used
I/O 
Configuration
GSI Technology
JEDEC Vendor 
ID Code
P
Bit #
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
X
X
X
X
0
0
0
0
0
0
0
0
0
0
X
X
X
X
0
0
0
0
0
0
0
0
0
0
0
1
1
x36
0
0
0
0
0
0
0
0
0
1
1
1
0
0
0 0 1 1 0 1 1 0 0 1
0 0 1 1 0 1 1 0 0 1
x18
Instruction Register
ID Code Register
·
31 30 29
Boundary Scan  Register
· · ·
· · ·
n
0
1
2
0
1
2
· · ·
0
1
2
· · ·
0
Bypass Register
TDI
TDO
TMS
TCK
Test Access Port (TAP) Controller