Open Access
Circuit Descriptions
3-23
ARM Development Board (ARM7TDMI Version)
Hardware Reference Guide
ARM DUI 0017C
3.2.17 Test Interface Controller and Connectors
This schematic is shown in
A.19 Test Interface Controller and Connecters
on page A-20.
The test interface comprises:
• a controller (U37), which is an ASB bus master
• four bi-directional transceivers (U38–41)
• two 20-way box headers (TEST1 and TEST2), which form the external connection.
Enabling the test interface
To enable the test interface, you must insert the link (LK17) marked “USE TIC”. If this link is
inserted, it is important to drive the test bus signals T_REQA, T_REQB and T_CLK.
Otherwise, the test interface controller may become the default bus master and the ARM
processor will not be able to gain control of the ASB.
In normal operation the test interface is not used and LK17 should be left out
.
For full details of the test interface refer to the
AMBA Specification
(ARM IHI 001).
3.2.18 Master Header Connectors and Level Convertors
This schematic is shown in
A.20 Master Header Connecters and Level Converters
on
page A-21.
Master header connectors
The ARM processor, mounted on a daughter card, is connected to the board using four
60-way connectors (PL6–9), as shown on this schematic. A number of the connector pins
are not used, as these are reserved for future expansion.
Level convertors
Because the board functions at 5V and the processor is a 3.3V component, level convertors
(U42–53) are provided to prevent high signal levels causing damage. These level convertors
are constructed from “Quickswitch” buffers. These devices have very low propagation delay
(less than 250ps) and appear as a 5 ohm resistor when switched on.
The output voltage for an input voltage equal to the supply is approximately 1V below
the supply. A resistor/diode network is used to provide a supply of 4.3V, so that high input
levels are clamped to 3.3V when driven out of the device.
Ref Name Description Options Default
LK17 USETIC enable the TIC out=disable, in=enable out
Table 3-14: LK17
hrg.book Page 23 Wednesday, July 22, 1998 9:18 AM
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