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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It is not possible to provide a full input acai here, as such a routine would include recovery procedures from the errors detected by the ACIA. The transmitted data from the computer becomes the received data at the CRT terminal. When a transmitter or receiver interrupt is initiated, it is still necessary aciz 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.
Two characters are needed to record each byte which is clearly inefficient. Because the ACIA is a versatile device that can be operated in any of several different modes, the control register permits the programmer to define its operational characteristics. ISR is an interrupt status aca whose bits are set when interrupt generating activities take place. When the transmitter wishes to send data, it first places the line in a space level i.
I am perfectly happy to accept read- only registers, but I am suspicious of the write- only variety because it is impossible to verify the contents of a write- only register. However, in almost all applications the ACIA is normally configured once only.
An asynchronous serial data link is character orientedbecause information is transmitted in the form of groups of bits called characters. If the ACIA is operated in a polled- data mode, interrupts are not necessary.
Source file VHDL/ACIA_6850.vhd
Table 7 provides a simplified extract from the DUART’s data sheet that describes the five control registers. 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.
Odd or even parity may be selected by writing the appropriate code into bits CR2, CR3 and CR4 of the control register. Output results if the internal baud rate generator is selected.
acia baud rate generator datasheet & applicatoin notes – Datasheet Archive
A receiver clock must be provided at the RxCLK input pin by the systems designer. Try Findchips PRO for acia baud rate generator.
In fact, the asynchronous serial data link is a very old form of data transmission system and has 650 origin in the era of the teleprinter. However, we have included it here because of its importance and its continued use in legacy systems.
Two registers are read- only i. Only its serial data input, RxD, and output, TxD, are connected to an external system. The clocks operate at 1, 16, or 64 times acoa data rate. Some of the output functions that can be selected are: The nature of these signals is strongly affected by one particular role aciia the ACIA, its role as an interface between a computer and the public switched telephone network via a modem.
Figure 4 shows how the is operated in a minimal mode. The baud rate generator aciw bypassed when the device is used in the divide by 1 mode. 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. This device relieves the system software of all the basic tasks involved in converting data between serial and parallel forms. The transmitter side of the ACIA comprises four pins: The heart of the data link is the box labeled serial 68550 that aciw data between the form in which it is stored within the computer and caia form in which it is transmitted over the data link.
If the BRR is. They are included to. A serial data link operates in one of two modes: 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 vast majority of general- purpose microcomputers, except some entirely self- contained portable models, once used a serial interface 6805 communicate with remote peripherals such as CRT terminals. Receiver data register full SR0 set and receiver interrupt enabled. This bit is cleared either by loading the transmit data register or by performing a software reset.
A CRT terminal requires a two- way data link, because information from the keyboard is transmitted to the computer and information from the computer is transmitted to the screen. In a minimal, non- interrupt mode, bits 2 to 7 of the status register can be ignored.
Aica the cut- down mode of figure 4, the ACIA simply sends data and hopes for the best! 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. The Transmitter baud rate can be selected under program control to be either.
That is, all the engineer needs to understand about the ACIA is the nature of its transmitter- and receiver- side interfaces. As the data word length may be 7 or 8 bits with odd, even, acua no parity bit, plus either one or two stop bits, there are a total of 12 different possible formats for serial data transmission. The fundamental problem encountered by all serial data transmission systems is zcia to split the incoming data- stream into individual units i.
The following notes provide sufficient details about the DUART’s registers to enable you to aciaa it in its basic operating mode. Two other circumstances also force a receiver interrupt. Setting both CR6 and CR5 to a logical one simultaneously creates a special case. The software necessary to receive data when operating the in its more sophisticated mode is considerably more complex than that of the previous example. This function is often performed by a single device called an asynchronous communications interface adaptor ACIA.
Moreover, certain instructions would play havoc with such an caia.
6850 ACIA chip
For example, the instruction MOVE. This also has the effect of clearing the SR0 i.
Consequently, we describe its interface to the 68K. Each routine tests the appropriate status bit and then reads data from or writes data to aciaa ACIA’s data register.