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82C55 PPI (1).ppt
- 2. About 82C55 The 82C55 is a popular low cost interfacing component, that can interface any TTL- compatible I/O device to a microprocessor. It is used to interface to the keyboard and a parallel printer port in PCs (usually as part of an integrated chipset).
- 3. About 82C55 PPI has 24 pins for I/O that are programmable in groups of 12 pins and has three distinct modes of operation.
- 4. 82C55 : Pin Layout Data bus Group : A Port (A0-A7) & Upper part of port C (C4-C7) Group : B Port (B0-B7) & Lower part of port C (C0-C3) Port A Port B Port C Programmi ng,reading & writing to a port Reset all program Input pin
- 6. Figure 1119 The 82C55 interfaced to the low bank of the 80386SX microprocessor.
- 7. A RESET input to the 82C55 initializes the device whenever the microprocessor is reset. A RESET input to the 82C55 causes all ports to be set up as simple input ports using mode 0 operation.
- 8. 82C55 PPI Addressing the 82C55 A1 A0 = 00 Port A ; = 01 Port B ; = 10 Port C ; = 11 Command Register;
- 9. Programming The 82C55 82C55 contains only two internal Command Registers Notice that bit position 7 selects either Command byte A or Command byte B. Command byte A : (command byte A programs the function of group A and B) Command byte B : (command byte b sets (1) or reset (0) bit of port C only if the 82C55 is programmed in mode 1 & 2)
- 10. Programming The 82C55 Group B Pins: Are programmed as either input or output pins.Group B can operate in either mode o or 1. Mode 0 is the basic input/output mode that allows pins of group B to be programmed as simple input latched output connections. Mode 1 operation is the strobed operation for group B connections.
- 11. Programming The 82C55 Group A Pins: Are also programmed as either input or output pins.The difference is that Group A can operate in modes 0,1 and 2. 82C55 has three operation modes: mode 0 mode 1 mode 2
- 13. Mode 0 (Basic Input/Output). This functional configuration provides simple input and output operations for each of the three ports. No handshaking is required, data is simply written to or read from a specified port.
- 14. MODE 1 (Strobed Input/Output) This functional configuration provides a means for transferring I/O data to or from a specified port in conjunction with strobes or handshaking signals. In mode 1, Port A and Port B use the lines on Port C to generate or accept these handshaking signals
- 15. Mode 1 Basic functional Definitions Two Groups (Group A and Group B). Each group contains one 8-bit data port and one 4-bit control/data port. The 8-bit data port can be either input or output Both inputs and outputs are latched. The 4-bit port is used for control and status of the 8-bit data port.
- 16. MODE 2 Basic Functional Definitions: Used in Group A only. One 8-bit, bi-directional bus port (Port A) and a 5-bit control port (Port C). Both inputs and outputs are latched. The 5-bit control port (Port C) is used for control and status for the 8-bit, bi- directional bus port (Port A).
- 17. A Stepper Motor Interfaced to the 82C55. Another device often interfaced to a computer system is the stepper motor. a digital motor because it is moved in discrete steps as it traverses through 360属 An inexpensive stepper motor is geared to move perhaps 15属 per step A more costly, high-precision stepper motor can be geared to 1属 per step.
- 18. In all cases, these steps are gained through many magnetic poles and/or gearing. Figure 1123 shows a four-coil stepper motor that uses an armature with a single pole. two coils are energized If less power is required, one coil may be energized at a time, causing the motor to step at 45属, 135属, 225属, and 315属. The motor is shown with the armature rotated to four discrete places, called full stepping. accomplished by energizing the coils, as shown A Stepper Motor Interfaced to the 82C55.
- 19. Figure 1123 The stepper motor showing full-step operation: (a) 45属 (b) 135属 (c) 225属 (d) 315属.
- 20. The motor is driven by NPN Darlington amp pairs to provide a large current to each coil. A circuit that can drive this stepper motor is illustrated in Fig 1124. with the four coils shown in place This circuit uses the 82C55 to provide drive signals used to rotate the motor armature in either the right- or left-hand direction. A Stepper Motor Interfaced to the 82C55.
- 21. Figure 1124 A stepper motor interfaced to the 82C55. This illustration does not show the decoder.
- 22. A Stepper Motor Interfaced to the 82C55. From subroutine of Ex 10-10, CX contain the direction and steps of rotation. If CX>8000h, motor spins in right hand direction If CX<8000h, motor spins in left hand direction The 15 bits except MSL(leftmost bit) express the no. of steps.