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CP82C55A Datasheet(PDF) 5 Page - Intersil Corporation |
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CP82C55A Datasheet(HTML) 5 Page - Intersil Corporation |
5 / 29 page 5 FN2969.10 November 16, 2006 two 4-bit ports under the mode control. Each 4-bit port contains a 4-bit latch and it can be used for the control signal output and status signal inputs in conjunction with ports A and B. See Figure 2B. Operational Description Mode Selection There are three basic modes of operation than can be selected by the system software: Mode 0 - Basic Input/Output Mode 1 - Strobed Input/Output Mode 2 - Bidirectional Bus When the reset input goes “high”, all ports will be set to the input mode with all 24 port lines held at a logic “one” level by internal bus hold devices. After the reset is removed, the 82C55A can remain in the input mode with no additional initialization required. This eliminates the need to pull-up or pull-down resistors in all-CMOS designs. The control word register will contain 9Bh. During the execution of the system program, any of the other modes may be selected using a single output instruction. This allows a single 82C55A to service a variety of peripheral devices with a simple software maintenance routine. Any port programmed as an output port is initialized to all zeros when the control word is written. FIGURE 2A. PORT A BUS-HOLD CONFIGURATION FIGURE 2B. PORT B AND C BUS-HOLD CONFIGURATION FIGURE 2. BUS-HOLD CONFIGURATION MASTER RESET OR MODE CHANGE INTERNAL DATA IN INTERNAL DATA OUT (LATCHED) EXTERNAL PORT A PIN OUTPUT MODE INPUT MODE RESET OR MODE CHANGE INTERNAL DATA IN INTERNAL DATA OUT (LATCHED) EXTERNAL PORT B, C OUTPUT MODE PIN P VCC FIGURE 3. BASIC MODE DEFINITIONS AND BUS INTERFACE DATA BUS 8I/O B PB7-PB0 4I/O PC3-PC0 4I/O C PC7-PC4 8I/O A PA7-PA0 CONTROL BUS ADDRESS BUS RD, WR 82C55A D7-D0 A0-A1 CS MODE 0 8I/O B PB7-PB0 CONTROL C 8I/O A PA7-PA0 MODE 1 OR I/O CONTROL OR I/O 8I/O B PB7-PB0 C BI- A PA7-PA0 MODE 2 CONTROL DIRECTIONAL FIGURE 4. MODE DEFINITION FORMAT D7 D6 D5 D4 D3 D2 D1 D0 PORT C (LOWER) 1 = INPUT 0 = OUTPUT PORT B 1 = INPUT 0 = OUTPUT MODE SELECTION 0 = MODE 0 1 = MODE 1 GROUP B PORT C (UPPER) 1 = INPUT 0 = OUTPUT PORT A 1 = INPUT 0 = OUTPUT MODE SELECTION 00 = MODE 0 01 = MODE 1 GROUP A 1X = MODE 2 MODE SET FLAG 1 = ACTIVE CONTROL WORD 82C55A |
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