QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 757A-A/-B ADDRESSABLE 2-WIRE BUS BUFFER LTC4302-1/LTC4302-2 DESCRIPTION Demonstration circuit 757-A/-B features the LTC4302- precharged to 1V to minimize bus disturbances. Two 1/LTC4302-2, an Addressable 2-Wire IC bus and SMBus general purpose input/output pins (GPIOs) on the compatible Bus Buffer. The LTC4302-1/LTC4302-2 al- LTC4302-1 can be configured as inputs, open-drain out- lows a peripheral board to be inserted and removed puts or push-pull outputs. The status of a GPIO is dis- from a live backplane without corruption of the bus. The played with an LED on the DC757-A/-B. The LTC4302-2 LTC4302-1/LTC4302-2 maintain electrical isolation be- option replaces one GPIO pin with a second supply volt- tween the backplane and peripheral board until their VCC age pin VCC2, providing level shifting between systems supply is valid and a master device on the backplane with different supply voltages. side addresses the LTC4302-1/LTC4302-2 and com- The DC757-A/-B is a part of the QuickEval systems mands them to connect. The LTC4302-1/LTC4302-2 which allows for quick and easy evaluation of the ADDRESS pin provides 32 possible addresses set by an LTC4302-1/LTC4302-2 with a software interface. external resistive divider between VCC and GND. The LTC4302-1/LTC4302-2 work with supply voltages rang- ing from 2.7V to 5.5V. The SDA and SCL inputs and out- Design files for this circuit board are available. Call puts do not load the bus lines when VCC is low. the LTC factory. Rise time accelerator circuitry allows for heavier capaci- tive bus loading while still meeting system timing re- quirements. During insertion, the SDA and SCL lines are OPERATION For operation with the DC757-A/-B, connect the back- can also read the internal registers of the LTC4302- plane side supply of 2.7V to 5.5V to Vcc (as shown in 1/LTC4302-2. Figure 1). For the DC757-B, with the LTC4302-2, con- The CONN pin, when pulled low, resets the LTC4302- nect the card side supply (2.7V to 5.5V) to VCC2. The 1/LTC4302-2 to its registers default state and disables backplane SDA and SCL are connected to SDAIN and communication to it. Communication can be reestab- SCLIN respectively while the card side bus lines are con- lished when CONN is released high. nected to SDAOUT and SCLOUT. The host controller on On the DC757-A/-B, the boards default values for resis- the backplane side first addresses and configures the tors R1 and R2 are 1.87kW and 2kW respectively and set LTC4302-1/LTC4302-2 to connect the backplane to card the address of the LTC4302-1/LTC4302-2 to (111 side. Communication between the backplane and card 0000) . For different addressing on multiple LTC4302- side components are then established and a host con- 2 1/LTC4302-2s daisy chained on the same back plane, the troller on either side can then control the LTC4302- resistors can be changed to values suggested in Table 1 1/LTC4302-2. Additional configurations include enabling of the data sheet. and disabling the rise time accelerators on the backplane side and/or the card side, setting the GPIO(s) to open- The DC757 can be configured for either a A or B. For drain output, push-pull output, or input mode, and set- a A board, U1 is an LTC4302-1, R13A pulls up the out- ting or resetting the GPIO(s) outputs. A host controller put lines and GPIOs to Vcc, and R13B and C2 are re- 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 757A-A/-B ADDRESSABLE 2-WIRE BUS BUFFER moved. To change to a B board, use an LTC4302-2 for connect the Vcc2 pin to the corresponding test turret. U1, remove R13A, R9 and D2, and add C2 and R13B to Figure 1. DC757-A/-B Equipment Setup respond with an Acknowledge. Select the address for QUICKEVAL SETUP the LTC4302-1/LTC4302-2 to be communicated with. The DC757-A/-B connects to the QuickEval USB Control- The LTC4302-1/LTC4302-2 has two Read/Write internal ler DC590A via 14-pin ribbon cable. The DC590A is registers. Checking a bit on the interface sets the corre- connected to a USB port on a PC. When the QuickEval sponding bit to a 1 and unchecking sets it to 0. The first software is opened, QuickEval will detect the DC757-A/- data byte is read when Read First is clicked or a bit in B and bring up the LTC4302-1/LTC4302-2 software in- the first register is changed. A two data byte read is car- terface (shown in Figure 2). Vcc is supplied from the ried out when Read Both is clicked or a bit in the second DC590A and an external supply is not needed. VCC2 register is changed. The status display for each bit is however will still require power on the DC757-B. updated after a read. Operation with the software interface starts with the se- The Live Running Bus check box enables a timer that lection of an address. Listed in the drop down menu are sends a bogus (0101 0101) data byte on the backplane 2 the 32 possible addresses for the LTC4302-1/LTC4302- bus lines every 100ms. This can be used for evaluation 2. By clicking the Find Address button, the software of the LTC4302-1/LTC4302-2 features. Connect a scope scans through the addresses and lists which addresses 2