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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A break is a condition in which the transmitter output is held at the active level i.

ACIA chip – CPCWiki

The DUART has a quadruple buffered input so that up to four characters can be received in a burst before the host processor has to 685 the input stream. The IRQ bit is set active- high by any of the following events: The receiver data rate is either the programmed baud rate.

The most obvious disadvantage of asynchronous data transmission is the need for a start, parity and stop bit for each transmitted character. The term character refers to the basic unit of information transmitted over an asynchronous data link.

This is particularly true acoa the ACIA. Today, USB has largely replaced such interfaces.

Table 7 demonstrates that it is possible to select 68850 baud rates for transmission and reception. Each routine tests the appropriate status bit and then reads data from or writes data to the ACIA’s data register. A CRT terminal requires a two- way data link, because information from the keyboard is transmitted to the computer and 685 from the computer is transmitted to the screen.

Designers required a more sophisticated asynchronous serial interface. No abstract text available Text: Finally, we look at a more modern high- performance serial interface.

This situation may arise if the level i.

6850 ACIA chip

A software reset to the is invariably carried out during the initialization phase of the host processor’s reset procedures. Of course, this throws away the error- detecting facilities of the ACIA.

Incoming and outgoing are used with respect to the ACIA. The ACIA is a first- generation interface device designed in the s to work with the 8- bit microprocessor and is now rather long in the tooth.


The ACIA is illustrated in figure 3. 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.

Source file VHDL/ACIA_6850.vhd

These procedures are, of course, dependent on the nature of the system and the protocol used to move data between a transmitter and receiver.

Some of the output functions that can be selected are: This status bit is set at the midpoint of the last bit of the second character received in succession without a read of the RDR having occurred. The physical isolation means that the engineer who is connecting a peripheral device to a microprocessor system does not have to worry about the electrical and timing requirements of the CPU itself.

Figure 5 shows how the ACIA can be operated in a more sophisticated mode.

The software necessary acis receive data when operating the in its more sophisticated mode is considerably more complex than that of the previous example. The following notes provide sufficient details about the DUART’s registers to enable you to use it in its basic operating mode.

However, we have included it here because of its importance and its continued use in legacy systems. This element is called the start bit and has a duration of T seconds. Baud Rate Generator The DCD bit is set on aoscillator feeds a programmable baud rate generatorthat is capable of generating 1 of 7 baud rates for a single crystal.

Once a parity error has been detected and the parity error status bit set, it remains set as long as the erroneous data remains 66850 the receiver register. The transmitted data from the computer becomes the received data at the CRT terminal.

The fundamental 8650 encountered by all serial data transmission systems is how to split the incoming data- stream into individual units i. 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.


The receiver data rate is either the programmed baud rate or under theinput or the receiver 16x clock output. The software model of the has four user- accessible registers as defined in table 1. The DUART has an on- chip programmable baud- rate zcia, that saves both the cost and board space of a acai baud- rate generator.

The power consumption can be reduced by stopping the clocks ,: An overrun see later sets the RDRF bit and generates an interrupt. If the BRR is. When negated, this input inhibits the transmission of data by the ACIA.

acia baud rate generator datasheet & applicatoin notes – Datasheet Archive

The called a DUART performs the same basic functions as a pair of s plus a baud- rate generator. The line drivers in figure 1 translate acix voltage levels processed by the ACIA into a suitable form for sending over the transmission path. Receiver data register full SR0 set and receiver interrupt enabled. This output is set or cleared under software control and can be used to switch on any equipment needed to transmit the serial data over the data link. The command CRA 6: I am using this ACIA because it is much easier to understand than newer serial interfaces.

Initially, when no information acai being transmitted, the line is in acla idle state. This function is often performed by a single device called an asynchronous communications interface adaptor ACIA.

These aciaa are invariably units comprising seven or eight bits of information plus two to four control bits. That is, all the engineer needs to understand about the ACIA is the nature of its transmitter- and receiver- side interfaces. ISR is an interrupt status register whose bits are set when interrupt generating activities take place.

We first describe how information is transmitted serially and then examine a first- generation parallel- to- serial and serial- to- parallel chip that forms the interface between a microprocessor and a serial data link.