View mb81c4256a datasheet:

( ) MB81C4256A 1/2 IL00 ********** C-MOS 1M-BIT DYNAMIC RAM -TOP VIEW- OE 1 24 A8 CAS 2 23 A7 D3 3 22 A6 D4 4 21 A5 5 GND 20 A4 VDD D1 8 17 (+5V) D2 9 16 A3 WE 10 15 A2 RAS 11 14 A1 *NC. 12 13 A0 = NC. NO CONNECTION ( ) MB81C4256A 2/2 13 A0 14 A1 A0-A8 ; ADDRESS INPUT 15 A2 CAS ; COLUMN ADDRESS STROBE 16 A3 D1-D4 ; DATA IN/OUT 20 8 A4 D1 OE ; OUTPUT ENABLE 21 9 A5 D2 RAS ; ROW ADDRESS STROBE 22 3 A6 D3 WE ; WRITE ENABLE 23 4 A7 D4 24 A8 CAS RAS OE WE 2 11 1 10 10 WE 2 CAS 11 RAS REF. CONT. ADDRESS RAS CLOCK CAS CLOCK WRITE CLK COUNTER GEN. GEN. GEN. 9 DATA COLUMN 9 4 4 IN DECODER 8,9,3,4 BUF. SENSE 4 4 D1-D4 13-16,20-24 AMP. A0-A8 99 DATA 512 ? 4 4 4 OUT BUF. 1,048,576 BITS