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XRT79L74 Datasheet(PDF) 7 Page - Exar Corporation |
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XRT79L74 Datasheet(HTML) 7 Page - Exar Corporation |
7 / 70 page PRELIMINARY XRT79L74 4 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC REV. P1.0.0 5 U26 RDY/DTACK O READY or DTACK: This active-low output pin will function as the READY output when the Microproces- sor Interface is configured to operate in the Intel Mode; and will function as the DTACK output when the Microprocessor Interface is running in the Motorola Mode. Intel Mode - READY output: When the Framer/UNI negates this output pin (e.g., toggles it "Low") it indicates to the Microprocessor that the current READ or WRITE operation is to be extended until this signal is asserted (e.g., toggled "High"). Motorola Mode - DTACK Data Transfer Acknowledge Output: The Framer/UNI will assert this pin in order to inform the Microprocessor that the present READ or WRITE cycle is nearly complete. If the Framer/UNI requires that the current READ or WRITE cycle be extended, then the Framer/UNI will delay its assertion of this signal. The 68000 family of Microprocessors requires this signal from its peripheral devices, in order to quickly and properly complete a READ or WRITE cycle. AF4 RESET I Reset Input: When this active-low signal is asserted, the Framer/UNI device will be asynchro- nously reset. When this occurs, all outputs will be tri-stated and all on-chip registers will be reset to their default values. AA26 µPCLK I Microprocessor Interface Clock Input: This clock input signal is used for synchronous/burst/DMA data transfer operations. This clock can be running up to 33MHz. AC23 WR/R/W I Write Strobe Intel Mode: If the Microprocessor Interface is configured to operate in the Intel Mode, then this active-low input pin functions as the WR (WRITE Strobe) input signal from the Micro- processor. Once this active-low signal is asserted, the Framer/UNI will latch the con- tents of the bi-directional data D[7:0] into the addressed registers or Buffer location within the Framer/UNI IC. R/W Input Pin Motorola Mode: When the Microprocessor Interface Section is operating in the Motorola Mode, then this pin is functionally equivalent to the R/W pin. In the Motorola Mode, a READ operation occurs if this pin is at a logic "1". Similarly a WRITE operation occurs if this pin is at a logic "0". AB22 AC22 AD22 PTYPE_0 PTYPE_1 PTYPE_2 I Microprocessor Type Select input: These three input pins are used to configure the Microprocessor Interface block to readily support a wide variety of Microprocessor Interfaces. The relationship between the settings of these input pins and the corresponding Microprocessor Inter- face configuration is presented below. "000" = Intel Asynchronous Mode "001" = Motorola Asynchronous Mode "111" = Power PC Mode AF22 DBEN I Bi-directional Data Bus Enable Input pin: If the Microprocessor Interface is operating in the Intel-I960 Mode, then this input pin is used to enable the Bi-directional Data Bus. Setting this input pin "Low" enables the Bi-directional Data bus. Setting this input "High" tri-states the Bi-directional Data Bus. PIN DESCRIPTIONS PIN #NAME TYPE DESCRIPTION |
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