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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When the transmitter wishes to send data, it first places the line in a space level i. Finally, the transmitter sends a stop bit at a mark level i. The clocks operate at 1, 16, or 64 times the data rate. Moreover, the DUART’s baud- rate generator can be programmed simply by loading an appropriate value into a clock select register.

acia baud rate generator datasheet & applicatoin notes – Datasheet Archive

They are included to. The five control registers are: Suppose you have a program with a bug that executes an unintended write to a write- only register. The error is due to the CPU not having read a character, rather than by any fault in the transmission and reception process. The ACIA is a byte- oriented device and can be interfaced to either the ‘s lower- order byte or to its upper- order byte. The RDRF bit is cleared either by reading the data in the receiver data register or by carrying out a software reset on the control register.

Similarly, the peripheral performs a logical isolation by hiding the details of information transfer across it. The framing error status bit is automatically cleared or set during the receiver data transfer time and is present throughout the time that the associated character is available.

6850 ACIA chip

I have included this material to demonstrate a the operation of asynchronous serial data links, and b the way in which memory- mapped peripherals are configured aciz accessed.

The term character refers to the basic unit of information transmitted over an asynchronous data link.

It is so called because the transmitted data and the received data are not synchronized over any extended period and therefore no special means of synchronizing the clocks at the transmitter and receiver is necessary.

The transmission path itself is normally a twisted pair of conductors which accounts for its very low cost. That is, the ACIA contains almost all the logic necessary to provide an asynchronous data link between a computer and an external system. Baud Rate Generator The crystal oscillator feeds a programmable baud rate generatorthat is capable of generating 1 of 7 baud rates for a single crystal.


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. Data- carrier- detect status bit SR2 set and receiver interrupt enabled. Two registers are read- only i. The format of the data word isselected if the internal baud rate generator is used as the receiver clock source. If no parity is selected, then both the ACIA’s transmitter parity generator and receiver parity checker are disabled.

This device relieves the system software of all the basic tasks involved in converting data between serial and parallel forms.

Try Findchips PRO for acia baud rate generator. The key to the operation of this type of link is both simple and ingenious.

Note that 6580 is a composite interrupt enable bit and enables all the three forms of receiver interrupt described above. The line drivers in figure 1 translate the voltage levels processed by the ACIA into a suitable form for sending over the transmission path.

This page describes a serial interface used to transmit serial data between a computer and a modem or a printer. The values below can be loaded into the appropriate clock- select register to select the following popular baud rates for both transmission and reception.

A serial data link operates in one of two modes: After this has been done, a single parity bit is calculated by the transmitter and sent after the data bits.

Figure 5 shows how the ACIA can be operated in a more sophisticated mode. Note that the serial interface is rarely used axia new equipment having been rendered obsolete by USB. Table 2 shows how the eight bits of the control register are grouped into four logical fields.

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

Source file VHDL/ACIA_6850.vhd

The heart of the data link is the box labeled serial interface that translates data between the form in which it is stored within the computer and the form in which it is transmitted over the data link. 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. Two other circumstances also force a receiver interrupt. The IRQ bit is set active- high by any of the following events: The software necessary to drive the ACIA in this minimal mode consists of three subroutines: 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 bit is cleared either by loading the transmit data register or by performing a software reset. This situation may arise if the level i. And this is before we consider that there are about seven commonly used values of T, the element duration.

ACIA chip – CPCWiki

The internal baud rate generator can be programmed tosame time one is being read by the processor. The ACIA has an internal baud rate generator. All the actions necessary to serialize the data and append start, parity and stop bits are carried out automatically i.

However, we have included it here because of its importance and its continued use in legacy systems.

One of the great advantages of peripherals like the ACIA is that they isolate the CPU from the outside world both physically and logically. The two items at the computer end of the data link enclosed in clouds in figure 1 represent the software components of the data link. However, in almost all applications the Aacia is normally configured once only.

The chip provides the data formattingdiagram of the circuit is illustrated in figure 1. Operation of the ACIA The software model of the has four user- accessible registers as defined in table 1.

The most daunting thing about many microprocessor interface chips is their sheer complexity. 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. The latter mode results if the internal acla rate generator is.