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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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 and accessed. After this has been done, a single parity bit is calculated by the transmitter and sent after the data bits. A serial data link operates in 66850 of two modes: 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.

ISR is an interrupt status register whose bits are set when interrupt generating activities take place. In a minimal, non- interrupt mode, bits 2 to 7 of the status register can be ignored. This operation can even be performed dynamically, if the need ever arises.

Incoming and outgoing are used with respect to the ACIA. You cannot detect the change by reading back the contents of the register. This bit is cleared either by loading the transmit data register or by performing a software reset.


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. Now the transmitter may send another character whenever it wishes. Data- carrier- detect status bit SR2 set and receiver interrupt enabled.

The ACIA has an internal baud rate generator. The software necessary to receive data when operating the in its more sophisticated mode is considerably more complex than that of the previous example. 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.

The latter mode is selected if the internal baud rate generatoronboard baud rate generator allows 16 different baud rates, for data transmission and reception timing. This element is called the start bit and has a duration of T seconds. Once a parity error has been detected and the parity error status bit set, it remains set as long as the erroneous data remains in the receiver register. Only its serial data input, RxD, and output, TxD, are connected to an external system. It is also possible to operate the ACIA in a minimal interrupt- driven mode.

A software reset to the is invariably carried out during the initialization phase of the host processor’s reset procedures.

Output bits can be programmed as: These procedures are, of course, dependent on the nature of the system and the protocol used to move data between a transmitter and receiver. Figure 4 shows how the is operated in a minimal mode. The ACIA is a byte- oriented device and can be interfaced to either the ‘s lower- order byte or to its upper- order byte. Transmitter data register empty SR1 set and transmitter interrupt enabled.


The transmitter side of the ACIA comprises four pins: The overrun bit is cleared after reading data from the RDR or by a software reset. The purpose of this exercise is two- fold.

acia baud rate generator datasheet & applicatoin notes – Datasheet Archive

International specifications cover this and other aspects of the data link. Operation of the ACIA The software model of the has four user- accessible registers as defined in table 1.

Using the ACIA The most daunting thing about many microprocessor interface chips is their sheer complexity. Table 7 demonstrates that it is possible to select independent baud rates for transmission and reception.

This input is intended for use in conjunction with a modem and, when low, indicates to the ACIA that the incoming data is valid. 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 receiver requests for service.

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 qcia data link.

The receiver data rate is determined by the programmed baud rate or by.