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FIN24CGFX Arkusz danych(PDF) 4 Page - Fairchild Semiconductor |
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FIN24CGFX Arkusz danych(HTML) 4 Page - Fairchild Semiconductor |
4 / 22 page www.fairchildsemi.com 4 Control Logic Circuitry The FIN24C has 4 signals that are selectable as 2 unidirectional inputs and 2 unidirectional outputs, or as 4 unidirectional inputs or 4 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 also pro- vides 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 when operating in Modes 1 and 3. When in Mode 2 the direction is controlled by both the DIRI and STROBE signals. Table 1 provides a complete description of the various 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 opera- tion the DIRO of the master device should be connected to the DIRI of the slave device. TABLE 1. Control Logic Circuitry When operating in a bi-directional mode the turn around func- tionality varies dependent upon 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 by the system designer to insure that no conten- tion occurs between the deserializer outputs and the other devices on this port. Optimally the peripheral device driving the serializer should be put into a HIGH Impedance state prior to the DIRI signal being asserted. When a device with dedicated data outputs turns from a deseri- alizer to a serializer the dedicated outputs will remain at the last logical value asserted. This value will only change 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 direction 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 will be the inversion of the DIRI signal. After power-up the DIRI and STROBE signal should initially both be HIGH. When STROBE goes LOW the device will be configured as a serializer and DIRO will be forced LOW. The device will remain as a serializer until the DIRI signal goes LOW. When DIRI goes LOW the device will be re-configured as a deserializer and the DIRO signal will be asserted HIGH. When operating the SerDes in pairs not all operating modes are compatible. Regardless of the mode of operation the serializer is always sending 24 bits of data and 2 word boundary bits. The deserializer is always receiving 24 bits of data and 2 word boundary bits. For some modes of operation not all of the data bits are valid due to some pins being dedicated inputs or out- puts. A value of “0” will be sent in the serial stream for all invalid data bits. 4-Bit Control Mode: When operating in 4-bit control mode the master device must be configured as MODE 2. (S2 = 1, S1 = 0) and the slave device must be con- figured as MODE 1 (S2 = 0, S1 = 1). When operat- ing in this mode 24 data and control bits can be sent from the master to the slave and 20 data bits can be sent from the slave to the master. Unidirectional con- trol signals should be connected to DP[21:24]. 2-Bit Control Mode: When operating in 2-bit control mode both devices must be configured in MODE 3 (S2 = S1 = “1”). In this mode of operation 22 bits can be sent in either direction. When operating in a 2-bit control mode serialized bits 21 and 22 will appear on outputs 23 and 24 of the deserializer. Mode Inputs Output Device Description Number S2 S1 STROBE DIRI DIRO State 0 0 0 x 0 1 na Power-Down State. The device will be powered x 1 0 na down and disabled regardless of all other signals 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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