Presentation on theme: "80286 Microprocessor and Supporting Chips"— Presentation transcript:
1 80286 Microprocessor and Supporting Chips Chapter 280286 Microprocessor and Supporting ChipsSection Microprocessor1. 68 pins2. LCC (leaded chip carrier) or PGA (pin grid array) package3. Real mode or Protected mode4. Power on real mode5. Power off to leave protected mode
6 Pins HOLD and HLDA (hold and hold acknowledge) 1. HOLD is used for DMA to request permission to use the buses.2. HLDA: Hold acknowledge RESET pin1. It stays high for at least 16 clocks.2. A20=1, A21=1, A22=1, A23=13. As long as the RESET pin is high, no instruction or bus activity is allowed.4. Enter into real mode
8 Pin INTR (interrupt request) expansion along with the 8259 interrupt controller chip Pin NMI (nonmaskable interrupt request) When this pin is activated, the will automatically perform INT 2. READY pinto insert a wait state for slow memory or I/O devices PEREQ and PEACK (processor extension request and acknowledge)used with the math processor 80287
9 BUSY pinBusy is an active-low input signal used by the math coprocessor to inform the 286 that it should stop program execution on WAIT and some ESC instruction. ERROR pinused by the math coprocessorINT 16 Vss pinVcc pin CAP pinA 0.047F capacitor (with 20%, 12V) must be connected between this pin and ground.
10 Section 2.2 82284 Clock Generator • and 8284 are not interchangeablePin description Pin F/C (frequency/crystal) Pin X1 and X2The frequency of the crystal must be twice the desired frequency of the system. Pin EFI (external frequency in)
12 Pin CLK (clock)The system will work on one-half of whatever frequency is assigned to CLK. Pin PCLK (peripheral clock)a 50% duty cycleclock generator.It has a frequency one-half that of the crystal or one-half of CLK. Pins S0, S1 (status signal)They are used for synchronization of PCLK and READY. Pin RES (reset)
16 Pin CLK (clock) Pins M/IO, S0, and S1 Pin READY Pins MB (multi bus mode) and CEN/AEN (command/address enable)Pass control of the system bus between the and DMA. Pin CMDLY (command delay)used along with READY to prolong the memory and I/O cycle time of the Pin CENL (command enable latch)connected to Vcc when there is onlt one bus controller in the system.
17 Pin ALE (address latch enable) due to the need for stable addresses in any system, ALE is used in the to latch the address into a 74XX373 latch. Pins IOWC, IORC, MWTC, MRDC Pin INTA (interrupt acknowledge) Pin DT/R (data transfer/receive) Pin DEN (data enable)for isolating the system data bus from the local data bus (for 74XX245) Pin MCE (master cascade enable)used with the 8259 interrupt controller chip to expand the number of hardware interrupts Pins Vcc (power) and GND (ground)
18 Section 2.4 80286 in IBM PC AT and ISA Buses IBM PC AT often refers to as ISA (Industry Standard Architecture) bus computers.80286 and the origin of the ISA BusesThe first IBM PC AT used80286822888228474ALS 245 (transceiver) , 74ALS573 (address latch), 74ALS244 (unidirectional bus buffer),Shown in Fig. 2-4.
19 A20 Gate and the case of high memory area (HMA) Address BusAddress bus A0-A19 is latched by 74ALS573 using the ALE signal.A20 Gate and the case of high memory area (HMA)A20 is gated into circuitry to allow it to overcome an anomaly associated with 286 and higher microprocessors.In 8086:+1FFFFFIn or higherFFFFF instead of 00000Here A20=1, How to solve it?