40 IOR lOW MEMR MEMW A NC EOP READY HLDA ADSTB A AEN 8237 HRQ Vcc CS DB CLK DB RESET DB2 DACK2 DB3 DACK3 DB4 DREQ3 DACKo DREQ2 DACK1 DREQ1 DB5 DREQo一 DB6 GND 20 21 DB71 4 0 8237 2 0 21 IOR IOW MEMR MEMW N C READY HLDA ADSTB AEN HRQ C S CLK RESET DACK2 DACK3 DREQ3 DREQ2 DREQ1 DREQ0 GND A7 A6 A5 A4 EOP A3 A2 A1 A0 Vcc D B0 D B1 D B2 D B3 D B4 DACK0 DACK1 D B5 D B6 D B7