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82C55A 数据表(PDF) 3 Page - Intel Corporation |
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82C55A 数据表(HTML) 3 Page - Intel Corporation |
3 / 23 page 82C55A 82C55A FUNCTIONAL DESCRIPTION General The 82C55A is a programmable peripheral interface device designed for use in Intel microcomputer sys- tems Its function is that of a general purpose IO component to interface peripheral equipment to the microcomputer system bus The functional configu- ration of the 82C55A is programmed by the system software so that normally no external logic is neces- sary to interface peripheral devices or structures Data Bus Buffer This 3-state bidirectional 8-bit buffer is used to inter- face the 82C55A to the system data bus Data is transmitted or received by the buffer upon execution of input or output instructions by the CPU Control words and status information are also transferred through the data bus buffer ReadWrite and Control Logic The function of this block is to manage all of the internal and external transfers of both Data and Control or Status words It accepts inputs from the CPU Address and Control busses and in turn issues commands to both of the Control Groups Group A and Group B Controls The functional configuration of each port is pro- grammed by the systems software In essence the CPU ‘‘outputs’’ a control word to the 82C55A The control word contains information such as ‘‘mode’’ ‘‘bit set’’ ‘‘bit reset’’ etc that initializes the func- tional configuration of the 82C55A Each of the Control blocks (Group A and Group B) accepts ‘‘commands’’ from the ReadWrite Control Logic receives ‘‘control words’’ from the internal data bus and issues the proper commands to its as- sociated ports Control Group A - Port A and Port C upper (C7 – C4) Control Group B - Port B and Port C lower (C3 – C0) The control word register can be both written and read as shown in the address decode table in the pin descriptions Figure 6 shows the control word format for both Read and Write operations When the control word is read bit D7 will always be a logic ‘‘1’’ as this implies control word mode information Ports A B and C The 82C55A contains three 8-bit ports (A B and C) All can be configured in a wide variety of functional characteristics by the system software but each has its own special features or ‘‘personality’’ to further enhance the power and flexibility of the 82C55A Port A One 8-bit data output latchbuffer and one 8-bit input latch buffer Both ‘‘pull-up’’ and ‘‘pull- down’’ bus hold devices are present on Port A Port B One 8-bit data inputoutput latchbuffer Only ‘‘pull-up’’ bus hold devices are present on Port B Port C One 8-bit data output latchbuffer and one 8-bit data input buffer (no latch for input) This port can be divided into 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 outputs and status signal inputs in conjunction with ports A and B Only ‘‘pull-up’’ bus hold devices are present on Port C See Figure 4 for the bus-hold circuit configuration for Port A B and C 3 |
类似零件编号 - 82C55A |
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类似说明 - 82C55A |
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