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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This clock may be either one-sixteen- or sixty- four times the rate at which bits are received at the data input terminal. Communications systems based on the have to change their baud rate by altering links on the board, making it tedious to change the baud rate frequently. The following notes provide sufficient details about the DUART’s registers to enable you to use it aciq its basic operating mode.
Source file VHDL/ACIA_6850.vhd
Odd or even parity may be selected by writing the appropriate code into bits CR2, CR3 and Aciia of the control register. Transmitter data register empty SR1 set and transmitter interrupt enabled. Moreover, the DUART’s baud- rate generator can be programmed simply by loading an appropriate value into a clock select register.
Table 7 provides a 68550 extract from the DUART’s data sheet that describes the five control registers. 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 line 8650 in figure 1 translate the voltage levels processed by the ACIA into a suitable form for sending over the transmission path.
6850 ACIA chip
Aica reader may be tempted to ask, “Why bother with a complex operating mode if the works quite happily in a basic mode? Bits CR0 and CR1 determine the ratio between the transmitted or received bit rates and the transmitter and receiver clocks, respectively.
Consequently, connecting one serial link with another may be difficult because so many options are available.
A unique feature is the inclusion of an on-chip programmable baud rate generatorcompatible to the EIA Stan dard RS specification. 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. Operation of the ACIA The software model of acai has four user- accessible registers as defined in table 1.
Note that the serial interface is rarely used in new equipment having been rendered obsolete by USB. This element aciia called the start bit and has a duration of T seconds.
Whenever the data link connects a CRT terminal to a computer few problems arise, as the terminal is itself character- oriented. Some of the output functions that can be selected are: Table 7 demonstrates that it is possible to select independent 66850 rates for transmission and reception.
ACIA chip – CPCWiki
We describe only the asynchronous data link because synchronous serial data links are best left to texts on networks. Designers required a more 68550 asynchronous serial interface. From the designer’s point of view, the ‘s hardware can be subdivided into three sections: A programmable Control Registerversions: The connection between the line drivers and transmission path is labeled plug and socket in figure 1 to emphasize that such mundane things as plugs become very important if interchangeability is required.
The eight possible data formats are given in table 2. 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.
These bits select also the type of parity if any and the number of stop bits. The overrun bit is cleared after reading data from the RDR or by a software reset. Consequently, the receiver overrun bit indicates that one or more characters in the data stream have been lost.
Figure 1 illustrates the basic serial data link between a computer and a CRT terminal. This bit is cleared either by loading the transmit data register or by performing a software reset.
The command CRA 6: Moreover, certain instructions would play havoc with such an arrangement.
Only its serial data input, RxD, and output, TxD, are connected to an external system. After this has been done, a single parity bit is calculated by the transmitter and sent after the data bits.
acia baud rate generator datasheet & applicatoin notes – Datasheet Archive
IUf the transmitter interrupt is enabled, an interrupt is generated by the transmitter whenever the transmit data register Aciaa is empty, signifying the need for new data from the CPU. One of the great advantages of peripherals like the ACIA is that they isolate the CPU from the outside world both physically and logically. As the data word length may be 7 or 8 bits with odd, even, or acai parity bit, plus either one or two stop bits, there are a total of 12 different possible formats for serial data transmission.