The ACIA is illustrated in figure 3. I am using this ACIA because it is much easier to understand than newer serial interfaces. Once you understand how the . MC Asynchronous Communications Interface Adapter (ACIA) F8DCh CPCI Serial Interface MC Control/Status Register (R/W). Computers transfer data in two ways. Parallel. Serial. Parallel data transfers often 8 or more lines are used to transfer data to a device that is only a few feet away.

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The eight possible data formats are given in table 2. This input is intended for use in conjunction with a modem and, when low, indicates to the ACIA that the incoming data is valid.

ACIA chip – CPCWiki

An asynchronous serial data link is character orientedbecause information is transmitted in the form of groups of bits called characters. The nature of these signals is strongly affected by one particular role of the ACIA, its role as an interface between a computer and the public switched telephone network via a modem.

If the Receiver clock uses the same baudonly other part zcia. Here, only the essential details of the ACIA’s transmitter and receiver sides are presented, because the way in which they function is described more fully when we come to the logical organization of the That is, the ACIA contains almost all the logic necessary to provide an asynchronous data link between a computer and an external system.

That is, all the engineer needs to understand about the ACIA is the nature of its transmitter- and receiver- side interfaces. A logical one in SR1 indicates that the contents of the transmit data register TDR have been sent to the transmitter and that the register is now ready for new data from the processor. Incoming and outgoing are used with respect to the ACIA. At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit.


The latter mode results if the internal baud rate generator is selected for receiver data. This is particularly true of the ACIA.

6850 ACIA chip

Once the DUART has been configured it can be used to transmit and receive characters exactly like the The peripheral- side interface 66850 the is divided into two entirely separate groups – the receiver group that forms the interface between the ACIA and a source of incoming data, and the transmitter group that forms the interface between the ACIA and the destination for outgoing data.

On top of this layer sits the application- level software, that uses the primitive operations executed by the lower- level software to carry out actions such as listing a file on the screen.

zcia The DUART has a full asynchronous bus interface which means that it supports asynchronous data transfers and can supply a vector number during an interrupt acknowledge cycle. Remember that these registers share the same address and that MR2A is selected automatically after MR1A has been loaded. Note that CR7 is a composite interrupt enable bit and enables all the three forms of receiver interrupt described above.

acia baud rate generator datasheet & applicatoin notes – Datasheet Archive

Each routine tests the appropriate status bit and then reads data from or writes data to the ACIA’s data register. For example, the OR instruction would read the contents of the ACIA’s status register, perform a logical OR and then write the result back to its control register. The receiver data rate scia either the programmed baud rate or under theinput or the receiver 16x clock output.


The framing error status bit, SR4, is set whenever the ACIA determines that a received character is incorrectly framed by a start bit and a stop bit. The Asynchronous Serial Interface The vast majority of general- purpose microcomputers, except some entirely self- contained portable models, once used a serial interface to communicate with remote peripherals such as CRT terminals.

This situation may arise if the level i. The eight bits of the read- only status register are depicted in table 3 and serve to indicate the status of both the transmitter and receiver portions of the ACIA at any instant. It shows that the address of the lower- order byte is odd, and that the pairs of read- only and write- only registers are separated by two i.

Output bits can be programmed as: The format of the data word isselected if the internal baud rate generator is used as the receiver clock source. However, if the data aciz is being used to, say, dump binary data to a magnetic tape, we run into a difficulty.

Often this complexity is more imaginary than real, because such peripherals are usually operated in only one of the many different modes that are software selectable.

Whenever the data link connects a CRT terminal to a computer few problems arise, as the terminal is itself character- oriented. Only its serial data input, RxD, and output, TxD, are connected to an external system. The transmitter side of the ACIA comprises four pins: Some sections of the ACIA are reset automatically by an internal power- on- reset circuit.