7 Data Bus 8088: AD0~AD7 8086: AD0~AD15 Address Bus (24pins) 8088: AD0~AD7, A8~A19 8086: AD0~AD15, A16~A19 AD means address and data are commonly used and separated by mux. ALE: Address Latch Enable to latch address signals
8 Pin Description BHE (bus high enable): to distinguish between the low byte and high byte of data. NMI (nonmaskable interrupt), edge-triggered INTR (interrupt request), active high level triggered CLOCK, need accurate clock signals RESET: after reset READY: insert wait state Test input from 8087 What is 8087? CSFFFFH DS0000H SS0000F ES0000H IP0000H FlagsClear QueueEmpty
9 Minimum/Maximum Mode MN/MX (pin 33) =5V to define pin 24 to pin 31 Used for the 8085 series
10 Pins 24-31 in maximum mode QS0 and QS1 (queue status, pins 24 and 25) S0, S1, and S2 (Status signals, pins 26, 27, and 28)
11 LOCK (pin 29) Used with “LOCK” prefix in the instruction to gain the control of the system bus (prevent DMA to control the bus when the instruction is under processing). LOCK MOV AX, Data RQ/GT0, RQ/GT1 (request/grant, pins 30, 31) These bidirectional pins allow another processor to gain control of the local bus. Pins 24-31 in Minimum Mode
18 Section 1.3 8284 Clock Generator and Driver Input pins: RES (reset in) X1 and X2 (crystal in): must be three times the desired frequency. IBM PC is 14.31818MHz F/C (frequency/clock select), select either the crystal input freq or EFI freq EFI (external frequency in) CSYNC (clock synchronization), allow several 8284 connected together RDY1 and AEN1, used as READY signal for inserting WAIT state.
19 RDY2 and AEN2, like RDY1 and AEN1 and are used for multiprocessing system. ASYNC Output signals RESET OSC (oscillator), provides the same frequency as the oscillator. CLK (clock), 1/3 of the crystal frequency and 33% duty cycle LCLOCK (peripheral clock), 1/2 CLK frequency, 50% duty cycle READY, for inserting WAIT cycle Duty cycle?