DS2109DK DS2109DK DS2109 Demo Board The DS2109DK is used in Plug and Play SCSI motherboards and host bus adapters to provide automatic active termination for 18 pairs of signal lines and is available in a 28–pin 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 SCSI–2 or SCSI–3 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 indicates 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 501–5007ES Switch PM Circuits Inc. D7789 C1 2.2 µF/16V tantalum capacitor Sprague 293–X225X9010A2T C2, C4 4.7 µF/10V tantalum capacitor Kemet T491A475K010AS C3, C5 0.1 µF/10V ceramic capacitor Kemet C1206C103K5RAC SMT Red LED Jlead Digikey P500 350 mW SOT23 2.7V Zener Digikey BZX84C2V7ZX 1/8W 5% 1.2K Resistor MEPCO 9C12063A1201JKR S1–3 L1–2 Z1 R1–2 022698 1/3 DS2109DK DS2109DK LAYOUT PDO LOW YES YES TERM PWR GND L1 S1 NO S2 NO GND DETECT Z1 L2 S3 FLOAT CURRENT SENSE RESET R1 R2 I/O REQ C/D SEL DB0 U1 DS2109S RST DB1 ACK DB2 BSY DB3 DB4 C2 DB7 J1 ATN DBP DB5 DB6 MSG C3 J2 C1 TP GND DB8 DBP1 DB9 DB10 U2 DS2109S DB15 DB14 DB11 DB13 DB12 C4 C5 DS2109DK DEMO DALLAS SEMICONDUCTOR CALL 214–450–8110 FOR INFO 022698 2/3 DS2109DK DS2109DK SCHEMATIC R1 Z1 2.7V L1 LED R2 1.2K C1 2.2 µf L2 LED J2 C2 4.7 µf C3 0.1 µf C5 0.1 µf U1 DS2109S U2 DS21507AE C4 4.7 µf S2 S3 J1 022698 3/3