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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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. When a transmitter or receiver interrupt is initiated, it is still necessary to examine the RDRF and TDRE bits of the status register to determine that the ACIA did indeed request the interrupt and to distinguish between transmitter and 6580 requests for service.

The latter mode results if the internal baud rate generator is. All the actions necessary to serialize the data and append start, parity and stop bits are carried out automatically i.

6850 ACIA chip

Consequently, connecting one serial link with another may be difficult because so many options are available. 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. Figure 1 illustrates the basic serial data link between a computer and a CRT terminal.

A software reset to the is invariably carried out during the initialization phase acua the host processor’s reset procedures. 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 680 and the parity error status bit set, it remains set aia long as the erroneous data remains in the receiver 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.


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 and accessed. As the data word length may be 7 or 8 bits with odd, even, or no parity bit, plus either one or two stop bits, there are a total of 12 different possible formats for serial data transmission.

ACIA chip – CPCWiki

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 wcia data from the processor.

The term character refers to the basic unit of information transmitted over an asynchronous data link. The transmitted data from the computer becomes the received data at the CRT terminal.

The fundamental problem encountered by all serial data transmission systems is how to split the incoming data- stream into individual units i. One of the first general- purpose interface devices produced by semiconductor manufacturers was the asynchronous communications interface adaptoror ACIA. The following fragment of code provides basic initialization, receive and transmit routines for the Aica.

Once the start bit has been detected, the receiver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receiver. This preference is not due to the high performance of a serial data link, but to its low- cost, simplicity and ease of use. An asynchronous serial data link is character orientedbecause information is transmitted in the form of groups of bits called characters.

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. When both these bits are high, a break is transmitted by the transmitter data output pin. The receiver data rate is either the programmed baud rate. The host computer has to read each character from a as it is received otherwise an overrun will occur and characters will be lost.

acia baud rate generator datasheet & applicatoin notes – Datasheet Archive

When the transmitter wishes to send data, it first places the line in a space level i. Operation of the ACIA The software model of the has four user- accessible registers as defined in table 1. The software necessary to receive data when operating the in its more sophisticated mode is considerably more complex than that of the previous example.


Two registers are read- only i. Status Register 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 wcia instant.

These data rates are very low indeed compared to USB rates. In most applications of the ACIA, the transmitter and receiver clocks are connected together and a common oscillator used for both transmitter and receiver sides of the ACIA. Note that the serial interface is rarely used in new equipment having been rendered obsolete by USB. Some aacia the output functions that can be selected are: Many modern ACIAs include on- chip receiver and transmitter clocks, relieving the system designer of the necessity of providing an additional external oscillator.

Source file VHDL/ACIA_6850.vhd

When the received character has been assembled, its parity is calculated and compared with the received parity bit following the character. In a minimal, non- interrupt mode, bits 2 to 7 of the status register can be ignored. Possibly the most common data format for the transmission of information between a processor and a CRT terminal is: 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.

This is a perfectly logical, indeed an elegant, thing to do. However, we have included it here because of its importance and its continued use in legacy systems.

Try Findchips PRO for acia baud rate generator. 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.