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FIN24AC Datasheet(PDF) 5 Page - Fairchild Semiconductor |
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FIN24AC Datasheet(HTML) 5 Page - Fairchild Semiconductor |
5 / 25 page © 2005 Fairchild Semiconductor Corporation www.fairchildsemi.com FIN24AC Rev. 1.0.3 5 Control Logic Circuitry The FIN24AC has the ability to be used as a 24-bit Seri- alizer or a 24-bit Deserializer. Pins S1 and S2 must be set to accommodate the clock reference input frequency range of the serializer. Table 1 shows the pin program- ming of these options based on the S1 and S2 control pins. The DIRI pin controls whether the device is a serial- izer or a deserializer. When DIRI is asserted LOW, the device is configured as a deserializer. When the DIRI pin is asserted HIGH, the device is configured as a serial- izer. Changing the state on the DIRI signal reverses the direction of the I/O signals and generates the opposite state signal on DIRO. For unidirectional operation, the DIRI pin should be hardwired to the HIGH or LOW state and the DIRO pin should be left floating. For bi- directional operation, the DIRI of the master device is driven by the system and the DIRO signal of the master is used to drive the DIRI of the slave device. Serializer/Deserializer with Dedicated I/O Variation The serialization and deserialization circuitry is setup for 24 bits. Because of the dedicated inputs and outputs, only 22 bits of data are ever serialized or deserialized. Regardless of the mode of operation, the serializer is always sending 24 bits of data and two boundary bits and the deserializer is always receiving 24 bits of data and two word boundary bits. Bits 23 and 24 of the serial- izer always contain the value of zero and are discarded by the deserializer. DP[21:22] input to the serializer is deserialized to DP[23:24] respectively. Turn-Around Functionality The device passes and inverts the DIRI signal through the device asynchronously 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 peripheral device driv- ing 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 deserial- izer and the values are overwritten. Power-Down Mode: (Mode 0) Mode 0 is used for powering down and resetting the device. When both of the mode signals are driven to a LOW state, the PLL and references are disabled, differen- tial input buffers are shut off, differential output buffers are placed into a HIGH-impedance state, LVCMOS outputs are placed into a HIGH-impedance state, LVCMOS inputs are driven to a valid level internally, and all internal circuitry is reset. The loss of CKREF state is also enabled to ensure that the PLL only powers up if there is a valid CKREF signal. In a typical application, signals do not change states other than between the desired frequency range and the power- down mode. This allows for system-level power-down functionality to be implemented via a single wire for a SerDes pair. The S1 and S2 selection signals that have their operating mode driven to a “logic 0” should be hard- wired to GND. The S1 and S2 signals that have their operating mode driven to a “logic 1” should be connected to a system level power-down signal. Table 1. Control Logic Circuitry Mode Number S2 S1 DIRI Description 0 0 0 x Power-Down Mode 1 0 1 1 24-Bit Serializer, 2MHz to 5MHz CKREF 0 1 0 24-Bit Deserializer 2 1 0 1 24-Bit Serializer, 5MHz to 15MHz CKREF 1 0 0 24-Bit Deserializer 3 1 1 1 24-Bit Serializer, 10MHz to 20MHz CKREF 1 1 0 24-Bit Deserializer |
Número de pieza similar - FIN24AC_07 |
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Descripción similar - FIN24AC_07 |
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