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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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LH540203D 데이터시트(PDF) 4 Page - Sharp Corporation |
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LH540203D 데이터시트(HTML) 4 Page - Sharp Corporation |
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4 / 17 page  OPERATIONAL DESCRIPTION (cont’d) Retransmit The FIFO can be made to reread previously-read data by means of the Retransmit function. A retransmit opera- tion is initiated by pulsing the RT input LOW. Both R and W must be deasserted (HIGH) for the duration of the retransmit pulse. The FIFO’s internal read-address pointer is reset to point to location zero, the first physical memory location, while the internal write-address pointer remains unchanged. After a retransmit operation, those data words in the region in between the read-address pointer and the write-address pointer may be reaccessed by subsequent read operations. A retransmit operation may affect the state of the status flags FF, HF, and EF, depending on the relocation of the read-address pointer. There is no restriction on the number of times that a block of data within an LH540203 may be read out, by repeating the retransmit operation and the subsequent read operations. The maximum length of a data block which may be retransmitted is 2048 words. Note that if the write-address pointer ever ‘wraps around’ (i.e., passes location zero more than once) during a sequence of retransmit opera- tions, some data words will be lost. The Retransmit function is not available when the LH540203 is operating in depth-cascaded mode, because the FL/RT control pin must be used for first-load selection rather than for retransmission control. Table 1. Grouping-Mode Determination During a Reset Operation XI FL/ RT MODE XO/HF USAGE XI USAGE FL/RT USAGE H 1 H Cascaded Slave 2 XO XI FL H 1 L Cascaded Master 2 XO XI FL L X Standalone HF (none) RT NOTES: 1. A reset operation forces XO HIGH for the nth FIFO, thus forcing XI HIGH for the (n+1)st FIFO. 2. The terms ‘master’ and ‘slave’ refer to operation in depth-cas- caded grouping mode. 3. H = HIGH; L = LOW; X = Don’t Care. Table 2. Expansion-Pin Usage According to Grouping Mode I/O PIN STANDALONE CASCADED MASTER CASCADED SLAVE I XI Grounded From XO (n-1st FIFO) From XO (n-1st FIFO) O XO/HF Becomes HF To XI (n+1st FIFO) To XI (n+1st FIFO) I FL/RT Becomes RT Grounded (Logic LOW) Logic HIGH Table 3. Status Flags NUMBER OF UNREAD DATA WORDS PRESENT WITHIN 2048 × 9 FIFO FF HF EF 0H H L 1 to 1024 H H H 1025 to 2047 H L H 2048 L L H LH540203 CMOS 2048 × 9 Asynchronous FIFO 4 |
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