INS8257 Datasheet | National Semiconductor

Description ;; The INS8257 is a Direct Memory Access (DMA) con- troller contained in a standard 40- pin dual- in- line The channel control registers consist of four 16- bit DMA address registers and four 16- bit terminal count 3 3 package. The chip, which is fabricated using (TC) registers. These registers provide the means for S» N- channel silicon gate technology, performs direct con- trolling DMA transfers on their respective C" control of high speed data transfers to and from channels. CD memory over four separate channels. Data can be transferred in single bytes or in blocks containing up The auto load feature permits the repetition of block c to 16,384 bytes. The INS8257 accepts requests for memory access transfers or the chaining of data blocks with a mini- mum of register initialization required. »3: from peripheral devices attached to its four DMA channels and acquires control of the system bus whenever the DMA request is honored. peting requests are resolved according to a programmable priority scheme (fixed or rotating). Program control of the INS8257 is exercised via a mode set register and four pairs of channel control Features - Four- Channel DMA Controller - Priority DMA Request Logic ..-a.g::.:s. CD registers (one pair per channel). A status register is also Included, which provides terminal count status - Channel Inhibit Logic for each channel. The status register also contains a - Terminal Count and Modulo 128 Outputs register programming flag, which is a valuable aid in maintaining byte synchronization when p Jogram- - Auto Load Mode ming channel control registers. - Single TTL Clock The mode set register contains f Ollr individual channel enable bits plus option select bits for the following options: rotating priority, extended write, TC stop and auto load. - Single + 5V Supply - Expandable - MICROBUSTM- patible INS8080 Family CPU Group MICROBUS Configuration A7- AO il Ji CKijl------I~1 OROO 1 _ - - - - - 1 ii Ac Ki...