DS2109DK
DS2109 Demo Board
DS2109DK
022698 1/3
The DS2109DK is used in Plug and Play SCSI mother-
boards and host bus adapters to provide automatic
active termination for 18 pairs of signal lines and is avail-
able in a 28pin SOIC package. The DS2109DK is a
demo board for both narrow and wide SCSI. A
DS21S07AE is used with the DS2109DK to terminate
27 lines for a SCSI2 or SCSI3 wide bus.
To use as a terminator for a narrow bus, connect the
SCSI cable into J2 of the DS2109DK. To use at the end
of a wide bus, connect to J1. Test points are available for
all of the SCSI bus signals. The TERM PWR LED indi-
cates termination power from the bus.
To demonstrate the automatic termination schemes of
the DS2109DK, connect cables to both J1 and J2. The
SCSI specifications require terminators installed in the
middle of the SCSI bus to be powered down or isolated
from the bus. The PDO LED will turn on when the
DS2109DK is isolated from the SCSI bus. The ground
detect method is controlled by switch GND DETECT.
Move the switch to YES, and if SCSI devices are
installed at both connectors, the PDO LED will come on.
The current sense method requires switch CURRENT
SENSE to be YES and then swtiching the RESET
switch from FLOAT to GND to FLOAT. This imitates a
SCSI reset from the host controller. If terminators are
connected to J1 and J2, the PDO LED will light. When
not demonstrating the automatic termination schemes,
leave switches S1 and S2 at NO and switch S3 at
FLOAT.
MATERIALS USED:
PART
DESCRIPTION
SOURCE
PART NUMBER
U1
Plug and Play SCSI Terminator
Dallas Semiconductor
DS2109S
U2
SCSI Active Terminator
Dallas Semiconductor
DS21S07AE
J1
Wide SCSI connector
Thomas and Betts
HFR068RA29BS1
J2
Narrow SCSI connector
Thomas and Betts
5015007ES
S13
Switch
PM Circuits Inc.
D7789
C1
2.2
F/16V tantalum capacitor
Sprague
293X225X9010A2T
C2, C4
4.7
F/10V tantalum capacitor
Kemet
T491A475K010AS
C3, C5
0.1
F/10V ceramic capacitor
Kemet
C1206C103K5RAC
L12
SMT Red LED Jlead
Digikey
P500
Z1
350 mW SOT23 2.7V Zener
Digikey
BZX84C2V7ZX
R12
1/8W 5% 1.2K Resistor
MEPCO
9C12063A1201JKR
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