
704886e62c7bafc10c37cc33933233af.ppt
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TK 2633 Introduction to Parallel Data Interfacing DR MASRI AYOB
Introduction MPU interface to external devices through both parallel and serial interfaces. Parallel data occur in system that use: Displays Keyboard Printers (old printer) Etc. Serial data occurs in: Some printers Data communications 2
8255 PIA (Peripheral Interface Adapter) 8255 can be programmed for data transfer in multipurpose mode, either as i/o or interrupt. It has 24 I/O pins, that can be divided into two groups of 8 -bit parallel ports: Port A and Port B, and the rest belong to Port C can be used as an individual bit or group of 4 -bit: CUPPER (CU) CLOWER (CL) Figure 1 shows 3 kind of port groups in 8255. 3
8255 A Programmable Peripheral Interface Figure 1. The pinout of the 8255 (PIA) PA 0 PA 1 PA 2 PA 3 PA 4 PA 5 PA 6 PA 7 D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 8255 RD WR A 0 A 1 RESET CS PB 0 PB 1 PB 2 PB 3 PB 4 PB 5 PB 6 PB 7 PC 0 PC 1 PC 2 PC 3 PC 4 PC 5 PC 6 PC 7 PORT A PORT B PORT C 4
8255 A Programmable Peripheral Interface 8255 A block diagram: Figure 2, shows two 8 -bit ports (A and B), two 4 bit ports (CU dan CL), data bus buffer and control logic. Figure 3 shows the table and pin configuration of 8255 and the equivalent circuit as control logic and input/output port. 5
Figure 2: 6
Figure 3: 7
8255 PIA Control Logic. RD (Read): This control signal is to enable read operation. When the signal is low activated, the MPU will read the data from certain I/O ports. WR (Write): This signal enable the write operation. When this signal is at logic low, the MPU will write to I/O ports or control registers. RESET (Reset): An active high signal. Use to clear the control register and sets all ports to input mode. Is connected to the RESET OUT pin of MPU. CS, A 0 and A 1: Signals to select device. CS is connected to a decoded address, whereas A 0 and 8 A 1 are connected to MPU address.
8255 PIA Control Logic. CS signal is a Master Chip Select, whereas A 0 and A 1 determine the input/output ports or control registers as tabulated in Table 1: The function of CS, A 0 and A 1 CS A 1 A 0 Selection 0 0 0 port A 0 0 1 port B 0 1 0 port C 0 1 1 Control Register 1 X X 8255 is disabled 9
8255 A PIA: Example Figure 4 10
8255 PIA Example: The port address as shown in Figure 4 is determined by CS, A 0 and A 1 pins. CS is active low when A 7 = 1 and A 6 to A 2 are at logic 0. When the signal is combined with A 0 and A 1, the port address is 80 H to 83 H as shown in Figure 5. 11
8255 PIA Example: Figure 5 12
8255 PIA Control Word: Figure 6 shows the function of control register, the content in this register is known as Control Word which determines input/output ports. This register is used to write control word when A 0 and A 1 are at logic 1. Bit D 7 in control register determines the I/O function or Set/Reset. If bit D 7 = 1, bits D 6 - D 0 determine the function of I/O in multiple modes as shown in Figure 6. Suppose bit D 7 = 0, • the port C operates in Bit Set/Reset (BSR) mode. • The BSR control word doest not cause any effect to port A and port B. • The port C command register sets (1) or resets (0) the port C pins during mode 1 or mode 2 operation. 13
8255 PIA Three main concept to communicate to 8255: • Determine the port address of A, B and C using CS, A 1 and A 0. • Write control word in control register. • Write I/O instructions to communicate with ports. 14
Functions of Control Word. Figure 6: 15
8255 Programmable Peripheral Interface Figure 8 shows the function of 8255, categorized in two mode: Set/Reset Bit (BSR) mode I/O mode. The BSR mode is used to set or reset bit at port C. Whereas the I/O is divided into 3 groups: Mode 0, Mode 1 and Mode 2. Mode 0, all ports function as input or output (I/O function). Mode 1, is handshake mod, where port A and/or port B used port C as handshake bit. Mode 2, port A can be used as bi-directional data transfer port with port C as handshake port and port B will be in mode 1 or mode 2. 16
8255 PIA Figure 8 17
8255 A Programmable Peripheral Interface Mode 0: Input / Output Mode In this mode port A and B use 8 -bit I/O data and port C uses two ports 4 -bit data. The characteristics of mode 0 are: • Output is latched. • Input does not latched. • Ports do not have the capability of handshake mode or interrupt mode. 18
8255 PIA : Mode 0: Input / Output Mode Example : • Determine the port address of circuit in Figure 9. • Determine the control word in Mode 0, in order to determine ports A and CU as output port and ports B and CL as input ports. • Write a program to read DIP switch and display the reading from port B to port A, from port CL to port CU. 19
Example : Figure 9: 20
8255 PIA: Example Solutions: Port Address : • It is actually an I/O memory map. • When A 15 is active high, Chip Select signal is activated. • Assuming all don’t care signals are at logic 0, therefore ports’ address are as follows: 21
8255 A Programmable Peripheral Interface Solution: Control Word: 22
8255 PIA Solution: ? ? ? 23
8255 PIA BSR (Bit Set/Reset) mode. The BSR mode will only affect to port C. Set/Reset can be determined by entering certain control word to control register. No change to the previous data when D 7 change from 1 to 0; therefore the I/O ports A and B unchanged. In BSR mode, the individual bit also can be used as ‘on / off’ switch. 24
8255 A Programmable Peripheral Interface BSR Control Word. The written control word in control register, set/reset will take only one bit at a time, as follows: 25
8255 PIA: BSR Mode Example: Write a BSR control word subroutine to set bit PC 7 and PC 3, and reset after 10 ms. Use the schematic diagram as shown below. 26
8255 A Programmable Peripheral Interface Solution: BSR Control Word: Port Address: • As shown in previous example : 83 H 27
8255 A Programmable Peripheral Interface Solution: Subroutine: Assuming that the delay subroutine has been determined earlier. 28
Thank you Q&A 29