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LH540215 Datasheet(PDF) 7 Page - Sharp Corporation |
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LH540215 Datasheet(HTML) 7 Page - Sharp Corporation |
7 / 48 page ![]() PIN DESCRIPTIONS (cont’d) PIN NAME PIN TYPE 1 DESCRIPTION LD Load I When LD is LOW, the data word on D0 – D17 (the data inputs) is written into a programmable-flag-offset register, or into the Control Register (when in the Enhanced Operating Mode), on the LOW-to-HIGH transition of WCLK, whenever WEN is LOW. (See Table 3.) Also, when LD is LOW, a word is read to Q0 – Q17 (the data outputs) from the offset registers and/or the Control Register (when in the Enhanced Operating Mode) on the LOW-to-HIGH transition of RCLK, whenever REN is LOW. (See again Table 3, and particularly the Notes following this table.) When LD is HIGH, normal FIFO write and read operations are enabled. FL /RT First Load/ Retransmit I In the standalone or paralleled configuration, FL/ RT should be LOW during a reset operation. (See Tables 1 and 2.) However, thereafter, in the standalone or paralleled configuration, if FL is taken HIGH, it functions instead as RT (Retransmit), and resets the FIFO’s internal read pointer to the first physical location of the RAM array. Note that although Retransmit is an ‘enhanced’ feature, it is always available for a FIFO during standalone operation, whether the FIFO is in IDT-Compatible Operating Mode or in Enhanced Operating Mode; it is not regulated either by the Control Register or by the EMODE control input. In IDT-compatible cascaded configuration, FL has an entirely different function; it is grounded for the first FIFO device (the ‘master’ device or ‘first- load’ device), and is set to HIGH for all other FIFO devices in the daisy chain. Thus, the Retransmit feature is not available for FIFOs operating in an IDT-compatible cascaded configuration. WXI /WEN2 Write Expansion Input/ Write Enable 2 I This signal is dual-purpose; its functionality is determined during a reset operation, according to its own state, and also according to the states of the three other control inputs RXI /REN2, FL/RT, and EMODE. (See Tables 1 and 2.) In the standalone or paralleled configuration, WXI/ WEN2 is grounded. In the cascaded configuration, WXI/ WEN2 is connected to WXO (Write Expansion Output) of the previous device, and functions as WXI. In the Enhanced Operating Mode, WXI/WEN2 functions as a second write-enable signal, WEN2, which is ANDed with WEN to produce an effective internal write-enable signal. 2 RXI /REN2 Read Expansion Input/ Read Enable 2 I This signal is dual-purpose; its functionality is determined during a reset operation, according to its own state, and also according to the states of the three other control inputs WXI /WEN2, FL/RT, and EMODE. (See Tables 1 and 2.) In the standalone or paralleled configuration, RXI/ REN2 is grounded. In the cascaded configuration, RXI/ REN2 is connected to RXO (Read Expansion Output) of the previous device, and functions as RXI. In the Enhanced Operating Mode, RXI/REN2 functions as a second read-enable signal, REN2, which is ANDed with REN – and perhaps also with OE, if Control-Register bit 05 is HIGH – to produce an effective internal read-enable signal. 2 FF Full Flag O When FF is LOW, the FIFO is full; further advancement of its internal write-address pointer, and further data writes through its Data Inputs into its internal memory array, are inhibited. When FF is HIGH, the FIFO is not full. FF is synchronized to WCLK. PAF Programmable Almost-Full Flag O When PAF is LOW, the FIFO is ‘almost full,’ based on the almost-full-offset value programmed into the FIFO’s Almost-Full Offset Register. The default value of this offset at reset is one-eighth of the total number of words in the FIFO-memory array, minus one, measured from ‘full.’ (See Table 4.) In the IDT-Compatible Operating Mode, PAF is asynchronous. In the Enhanced Operating Mode, PAF is synchronized to WCLK after a reset operation, according to the state of Control Register bit 04. (See Table 5.) NOTES: 1. I = Input, O = Output, Z = High-Impedance, V = Power Voltage Level 2. The ostensible differences in signal assertiveness are reconciled before ANDing. BOLD ITALIC = Enhanced Operating Mode 512 x 18/1024 x 18 Synchronous FIFO LH540215/25 7 |
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