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1、wordA parallel output controller (POC) 04008603 PurposeThe purpose of this project is to design and simulate a parallel output controller (POC)which acts an interface between system bus and printer.The Alteras Maxplus IIEDA tool is remended and provided for simulation. Please refer to William,Stalli
2、ngs.“puter Organization and Architecture, Designing for Performance, P.6980; P.190194.Tasks POC is one of the most mon I/O modules, namely the parallel output controller. It plays the role of an interface between the puter system bus and the peripheral (such as a printer or other output devices). Fi
3、gure 1 Printer ConnectionFigure 1shows the connecting of a printer to the system bus through the POC. The munication between POC and the printer is controlled by a “handshake protocol illustrated inFigure 2. Figure2 The handshake-timing diagram between POC and the printerThe handshaking process is d
4、escribed as follows: When the printer is ready to receive a character, it holds RDY=1.The POC must then hold a character at PD (parallel data) port and produce a pulse at the terminal TR (transfer request). The printer will change RDY to 0, take the character at PD and hold the RDY at 0 until the ch
5、aracter has been printed (e.g. 5 or 10ms), then set RDY=1 again when it is ready to receive the next character. (Suppose the printer has only a one character “buffer register, so that each character must be printed before the next character is sent).In order to ease your design work, the further exp
6、lanations of the POC operations and some design hints are given as follows:The buffer register BR is used to hold a character that has been sent via the system bus while that the character is being transferred to the printer. The status register SRis used for two control functions:SR7serves as a rea
7、dy flag for system bus transfers to BR (like the printer RDY signal for transfers from POC to the printer), and SR0 is used to enable or disable interrupt requests from POC. If SR0=1, then POC will interrupt when it is ready to receive a character (i.e., when SR7=1). If SR0=0, then POC will not inte
8、rrupt. The other bits of SR are not used and empty.The transfer of a character to POC via the system bus proceeds as follows. POC indicates that it is ready by setting SR7.The processor reads SR (by executing a polling or interrupt service routine) and, finding SR7=1, writes a character to BR. The P
9、OC clears SR7 when it loads this character into BR to indicate that another character should not be sent for the moment. POC then proceeds to transfer the character in BR to the printer by generating a pulse at TR. The processor, in the meantime, continues to fetch and execute instructions .If it sh
10、ould happen to read SR, it will find SR7=0 and hence will not attempt to send another character to the printer. When the printer isready to receive another character, POC sets SR7.The transfer cycle can now repeat. The overall connection of printer and POCThe overall connectiongraph as follows:The t
11、wo main modules: Block1 (printer) and pocSimulation and Explain1、The simulation waves of Block1(the printer)2、The simulation waves of pocRW is an input signal that control the transmission of data from CPU to POC.RDYis an input signal which is the ready message transferred from printer to POC.CS is
12、an enable signal.TR is a pulse signal to make the RDY bee low-level. clk is a clock signal. Irq is a interrupt signal from poc to processor. DATA is a input signal of 8 bits.PD is a 8 bits signal from POC to Printer.Explain: We can see that when CS is high level and RDY is high, the printer is free.
13、POC gives an interrupt signal to CPU and the data transfers to POC when RW is high level. Then the data will be transferred to printer as long as the printer is free. Inthe duration of the transmition of data, the POC send a TRpulse to indicate that it want to transfer data to the printer, The print
14、er then changesRDY to 0, take the character at PD and hold the RDY at 0 until the character has been printed.2、The simulation waves of poc connected with the printerExplain:When CS=1 and RW is also high level, it indicates that there are some data to be printed. If the printer is free, the poc will
15、generate an interrupt (IRQ=1) to finish the transmition of data from processor to the poc.After processor have dealed with the interrupt, the data will be transferred to printer. Conclusions and discussionsIn our project the poc can work corectly. But in this model,it reduces the efficiency of the p
16、oc that one printer can only be used by one user . We can make the interrupts generated by many users in order using some techniques to solve this problem.Appendixlibrary ieee;use ieee.std_logic_1164.all;use ieee.std_logic_unsigned.all;entity poc isport(RDY:IN STD_LOGIC;DATA:IN STD_LOGIC_VECTOR(7 DOWNTO 0);PD:OUT STD_LOGIC_VECTOR(7
