Debug Support
ARM DDI 0144B
Copyright 1999, 2000 ARM Limited. All rights reserved.
8-23
During SHIFT-DR, a data value is shifted into the serial register. Bits 32 to 36 specify
the address of the EmbeddedICE unit register to be accessed.
During UPDATE-DR, this register is either read or written depending on the value of
bit 37 (0 = read).
The EmbeddedICE register map is shown in
Control registers
on page 8-41.
Scan chain 3
Purpose
Allows the ARM940T to control an external boundary scan chain.
Length
User-defined
Scan chain 3 is provided so that an optional external boundary scan chain can be
controlled using the ARM940T. Typically this is used for a scan chain around the pad
ring of a packaged device. The following control signals are provided and are generated
only when scan chain 3 has been selected. These outputs are inactive at all other times:
DRIVEOUTBS
This is used to switch the scan cells from system mode to test
mode. This signal is asserted whenever an INTEST, EXTEST,
CLAMP, or CLAMPZ instruction is selected.
PCLKBS
This is the update clock, generated in the UPDATE-DR state.
Typically the value scanned into the chain is transferred to the cell
output on the rising edge of this signal.
ICAPCLKBS, ECAPCLKBS
These are the capture clocks used to sample data into the scan cells
during INTEST and EXTEST respectively. These clocks are
generated in the CAPTURE-DR state.
SHCLK1BS, SHCLK2BS
These are non-overlapping clocks generated in the SHIFT-DR
state that are used to clock the master and slave element of the
scan cells respectively. When the state machine is not in the
SHIFT-DR state, both these clocks are LOW.
RSTCLKBS
This signal is used to reset the cells of the Boundary Scan Chain
when
nTRST
is asserted or the TAP controller state machine is in
the reset state.
In addition to these control outputs,
SDINBS
outputs and
SDOUTBS
inputs are
provided to support external scan chains. When an external scan chain is in use,
SDOUTBS
must be connected to the serial data output of the external chain and
SDINBS
must be connected to the serial data input of the external chain.