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 element is called the start bit and has a duration of T seconds. The latter mode results if the internal baud rate generator is selected for receiver data.
One of the first general- purpose interface devices produced by semiconductor manufacturers was the asynchronous communications interface adaptoror ACIA. Moreover, the DUART’s baud- rate generator can be programmed simply by loading an appropriate value into a clock select register.
Possibly the most common data format for the transmission of information between a processor and a CRT terminal is: 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.
The latter mode results if the internal baud rate generator is. Consequently, the receiver overrun bit indicates that one or more characters in the data stream have been lost. This is a perfectly logical, indeed an elegant, thing to do.
Consequently, we describe its interface to the 68K.
6850 ACIA chip
You can load CRA with 0A 16 to disable both channels during its setting up phase and then load it with 05 16 to enable its transmitter and receiver ports once its other registers have been set up. The values below can be loaded into the appropriate clock- select register to select the following popular baud rates for both transmission and reception.
The command CRA 6: No abstract text available Text: 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 1 illustrates the basic serial data link between a computer and a CRT terminal. This input is intended for use in conjunction with a modem and, when low, indicates to the ACIA that the incoming data is valid.
In a minimal, non- interrupt mode, bits 2 to 7 of the status register can be ignored. IMR is an interrupt mask register whose bits are set by the programmer to enable an interrupt, or cleared to mask the interrupt. The key to the operation of this type of link is both simple and ingenious.
In the cut- down mode of figure 4, the ACIA simply sends data and hopes for the best!
ACIA chip – CPCWiki
Output bits can be programmed as: The baud rate generator is bypassed when the device is used in the divide by 1 mode. You cannot detect the change by reading back the contents of the register. However, in almost all applications the ACIA is normally configured once only. Bits CR0 and CR1 determine the ratio between the transmitted or received bit rates and the transmitter and receiver clocks, respectively.
That is, all the engineer needs to understand about the ACIA is the nature of its transmitter- and receiver- side interfaces.
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 material is taken from articles I wrote on the 68K microprocessor. The receiver data rate is either the programmed baud rate or under theinput or the receiver 16x clock output. This operation can even be performed dynamically, if the need ever arises.
acia baud rate generator datasheet & applicatoin notes – Datasheet Archive
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. We describe only the asynchronous data link because synchronous serial data links are best left to texts on networks.
The reader may be tempted to ask, “Why bother with a complex operating mode if the works quite happily in a basic mode? Whenever the data link connects a CRT terminal to a computer few problems arise, as the terminal is itself character- oriented.