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8279 – Programmable Keyboard/Display Interface,[object Object],IIE - SAP ,[object Object]
WHY 8279???,[object Object],WHAT WE KNOW,,[object Object],[object Object]
The disadvantages of this method of interfacing keyboard and display is that the processor has to refresh the display and check the status of the keyboard periodicallyusing polling technique.,[object Object],[object Object]
Intel’s 8279 is a general purpose keyboard displaycontroller that simultaneously drives the display of a,[object Object],system and interfaces a keyboard with the CPU, leaving it,[object Object],free for its routine task.,[object Object],IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
Architecture ,[object Object],of ,[object Object],8279,[object Object],IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
2 key lock out,[object Object],WHAT IS ,[object Object],??,[object Object],IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
2 key lock out,[object Object],WHAT IS ,[object Object],N – key roll over,[object Object],??,[object Object],IIE - SAP ,[object Object]
IIE - SAP ,[object Object]
Scanned Keyboard Special Error Mode :,[object Object],[object Object]
This mode is programmed using end interrupt / error mode set command.
If during a single debounce period ( two keyboard scans ) two keys are found pressed , this is considered a simultaneous depression and an error flag is set.
This flag, if set, prevents further writing in FIFO butallows the generation of further interrupts to the CPU,[object Object],for FIFO read. ,[object Object],[object Object],the FIFO status word. The error Flag is reset by sending,[object Object],normal clear command with CF = 1.,[object Object],IIE - SAP ,[object Object]
Scanned Sensor Matrix : ,[object Object],[object Object]
 The sensor codes are stored in the CPU addressable sensor RAM.
 In the sensor matrix mode, the debounce logic is inhibited. The 8-byte FIFO RAM now acts as 8 * 8 bit memory matrix.
The status of the sensor switch matrix is fed directly to sensor RAM matrix. Thus the sensor RAM bits contains the rowwise and column wise status of the sensors in the sensor matrix.
 The IRQ line goes high, if any change in sensor value is detected at the end of a sensor matrix scan or the sensor RAM has a previous entry to be read by the CPU.
 The IRQ line is reset by the first data read operation, if AI = 0, otherwise, by issuing the end interrupt command. AI is a bit in read sensor RAM word.IIE - SAP ,[object Object]
Strobed input: ,[object Object],[object Object],IIE - SAP ,[object Object]
IIE - SAP ,[object Object]

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8279 in microprocessor

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  • 26.
  • 27. This mode is programmed using end interrupt / error mode set command.
  • 28. If during a single debounce period ( two keyboard scans ) two keys are found pressed , this is considered a simultaneous depression and an error flag is set.
  • 29.
  • 30.
  • 31. The sensor codes are stored in the CPU addressable sensor RAM.
  • 32. In the sensor matrix mode, the debounce logic is inhibited. The 8-byte FIFO RAM now acts as 8 * 8 bit memory matrix.
  • 33. The status of the sensor switch matrix is fed directly to sensor RAM matrix. Thus the sensor RAM bits contains the rowwise and column wise status of the sensors in the sensor matrix.
  • 34. The IRQ line goes high, if any change in sensor value is detected at the end of a sensor matrix scan or the sensor RAM has a previous entry to be read by the CPU.
  • 35.
  • 36.
  • 37.
  • 38.
  • 39.
  • 40.
  • 41. PPPPP is a 5-bit binary constant.
  • 42.
  • 43.
  • 44. In scanned keyboard mode, AI and AAA bits are of no use. The 8279 will automatically drive data bus for each subsequent read, in the same sequence, in which the data was entered.
  • 45. In sensor matrix mode, the bits AAA select one of the 8 rows of RAM.
  • 46.
  • 47.
  • 48. AI is auto increment flag and AAAA, the 4-bit address points to the 16-byte display RAM that is to be read.
  • 49. If AI=1, the address will be automatically, incremented after each read or write to the Display RAM.
  • 50.
  • 51.
  • 52.
  • 53. The output lines are divided into two nibbles ( OUTA0 – OUTA3 ) and (OUTB0 – OUTB3 ), those can be masked by setting the corresponding IW bit to 1.
  • 54. Once a nibble is masked by setting the corresponding IW bit to 1, the entry to display RAM does not affect the nibble even though it may change the unmasked nibble.
  • 55. The blank display bit flags (BL) are used for blanking A and B nibbles.
  • 56. D0, D2 corresponds to OUTB0 – OUTB3
  • 57. D1, D3 corresponds to OUTA0 - OUTA3 for blanking and masking.
  • 58. If the user wants to clear the display, blank (BL) bits are available for each nibble as shown in format.
  • 59.
  • 60.
  • 61. If CD2 = 0, the clear display command is invoked by setting CA(CLEAR ALL) =1 and maintaining CD1, CD0 bits exactly same as above.
  • 62. If CF(CLEAR FIFO RAM STATUS) =1, FIFO status is cleared and IRQ line is pulled down and the sensor RAM pointer is set to row 0.
  • 63.
  • 64.
  • 65. Otherwise, if a change in sensor value is detected, IRQ goes high that inhibits writing in the sensor RAM.
  • 66.
  • 67.
  • 68.