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FIN24C Datasheet(PDF) 5 Page - Fairchild Semiconductor |
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FIN24C Datasheet(HTML) 5 Page - Fairchild Semiconductor |
5 / 25 page ©2005 Fairchild Semiconductor Corporation www.fairchildsemi.com FIN24C Rev. 1.0.2 5 Control Logic Circuitry The FIN24C has four signals that are selectable as two unidirectional inputs and two unidirectional outputs, or as four unidirectional inputs or four unidirectional outputs. These are often used by applications for control signals. The mode signals S1 and S2 determine the direction of the DP[21:24] data signals. The 00 state provides for a power-down state where all functionality of the device is disabled or reset. The DIRI terminal controls the direc- tion of the device in Modes 1 and 3. When in Mode 2, the direction is controlled by both the DIRI and STROBE sig- nals. Table 1 provides a complete description of the vari- ous modes of operation. For unidirectional operation, the DIRI terminal should be hardwired to a valid logic level and the DIRO terminal should be left floating. For bi- directional operation, the DIRO of the master device should be connected to the DIRI of the slave device. When operating in a bi-directional mode, the turn-around functionality is dependent on the mode of the device. For Modes 1 and 3, the device asynchronously passes and inverts the DIRI signal through the device to the DIRO signal. Care must be taken during design to ensure that no contention occurs between the deserializer outputs and the other devices on this port. Optimally the periph- eral device driving the serializer should be in a HIGH- impedance state prior to the DIRI signal being asserted. When a device with dedicated data outputs turns from a deserializer to a serializer, the dedicated outputs remain at the last logical value asserted. This value only changes if the device is once again turned around into a deserializer and the values are overwritten. When the device is in Mode 2 (S2 = 1, S1 = 0), the direc- tion of operation is dependent upon both the STROBE signal and the DIRI signal. At power-up, the mode select signals are both LOW and the DIRO signal is the inver- sion of the DIRI signal. After power-up, the DIRI and STROBE signal should initially both be HIGH. When STROBE goes LOW the device is configured as a serial- izer and DIRO will be forced LOW. The device remains a serializer until the DIRI signal goes LOW. When DIRI goes LOW, the device is re-configured as a deserializer and the DIRO signal is asserted HIGH. When operating the SerDes in pairs, not all operating modes are compatible. Regardless of the mode of oper- ation, the serializer is always sending 24 bits of data and two word boundary bits. The deserializer is always receiving 24 bits of data and two word boundary bits. For some modes of operation, not all of the data bits are valid because some pins are dedicated inputs or outputs. A value of “0” is sent in the serial stream for all invalid data bits. Table 1. Control Logic Circuitry Mode Number Inputs Output Device State Description S2 S1 STROBE DIRI DIRO 0 0 0 x 0 1 na Power-Down State. The device is powered down and disabled regardless of all other signals. x1 0 na 1 0 1 x 0 1 Des 4-Bit Unidirectional Control Mode DP[21:24] are outputs x1 0 Ser 2 1 0 0 0 1 Des 4-Bit Unidirectional Control Mode DP[21:24] are inputs STROBE and DIRI operate as an RS-Latch to change the state of operation. In general, DIRI and Strobe should not be LOW at the same time. 01 0 Ser 10 1 Des 1 1 DIRO (n-1) Previous 3 1 1 x 0 1 Des 2-Bit Unidirectional Control Mode DP[21:22] are Inputs DP[23:24] Outputs 1 1 x 1 0 Ser 2-Bit Unidirectional Control Mode DP[21:22] are Inputs DP[23:24] Outputs |
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