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HW4soln-3750-F09b

# HW4soln-3750-F09b - EE 3750 HW 4 solutions 1 EE 3750...

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EE 3750 — HW 4 solutions 1 EE 3750 — Homework 4 solutions Fall 2009 1. (a) Brey, Chapter 9, Problem 11 - When does ALE float to its high-impedance state? (b) Brey, Chapter 9, Problem 27 - What 8086/8088 signal is used to select the direction of the data flows through the 74LS245 bidirectional bus buffer? (a) Never. (b) The DT / R signal (data transmit/receive) controls the direction of data flow through the bi-directional bus buffer. See Figure 9-6 for an illustration of the connections. 2. Write an 8086 instruction sequence to use program-controlled I/O to output words from array black . The words are signed integers, and output a word only if its value is 3750. Output a total of 120 words. Let outdev denote the output device. The status port for outdev is a byte port at address 52B0H; bit 4 is the ready bit. The data port for outdev is a word port at address 52B2H. STATUS EQU 52B0H DATA EQU 52B2H MOV CX, 120 ; loop counter MOV BX, 0 ; initialize pointer into black TOP: MOV DX, STATUS ; use DX because port addresses longer than 8 bits CKRDY: IN AL, DX TEST AL, 10000B JZ CKRDY AGAIN: MOV AX, BLACK[BX] ADD BX, 2 ; update pointer (whether or not element of black has value 3750) CMP AX, 3750 ; check value of element of black JL AGAIN ; if < 3750, then try again with next element of black MOV DX, DATA ; if 3750, then output OUT DX, AX LOOP TOP ; only reaches the LOOP instruction after an output, so will output exactly 120 times before exiting 3. Write an 8086 instruction sequence to initialize an 82C55 programmable peripheral interface. Set Group A to operate in Mode 1 with Port A as an output port. Set Group B to operate in Mode 1 with Port B as an input port.

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