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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A unique feature is the inclusion of an on-chip programmable baud rate generatorcompatible to the EIA Stan dard RS specification.
Initially, when no information is being transmitted, the line is in an idle state.
No abstract text available Text: IMR is an interrupt mask register whose bits are set by the programmer to enable an interrupt, or cleared to mask the interrupt. Moreover, the DUART’s baud- rate generator can be programmed aciq by loading an appropriate value into a clock select register.
Afterwards, a secondary reset can be performed by software, as we shall describe later. The clocks operate at 1, 16, or 64 times the data rate. A less obvious disadvantage is due to the character- oriented nature of the data link. Setting both CR6 and CR5 to a logical one simultaneously creates a acis case. The baud rate generator is bypassed when the device is used in the divide by 1 mode. The serial interface, that moves information from point- to- point one bit at a time, is generally preferred to the parallel interface, that is able to move a group of bits simultaneously.
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.
acia baud rate generator datasheet & applicatoin notes – Datasheet Archive
Finally, the transmitter sends a stop bit at a mark level i. Output bits can be programmed as: Table 7 demonstrates that it is possible to select independent baud rates for transmission and reception. The eight possible data formats are given aacia table 2. For example, in Morse code the dots and dashes of a character are separated by an inter- symbol space, whereas the individual characters are separated by an inter- character space acoa is three times the duration of an inter- symbol space.
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. The software necessary to drive the ACIA in this minimal mode consists of three subroutines: 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.
The line drivers in figure 1 translate the voltage levels processed by the ACIA into a suitable form for sending over the transmission path. The transmission path itself is normally a twisted pair of conductors which accounts for its very low cost.
The nature of these signals is strongly affected by one particular role of the Aia, its role as an interface between a computer and the public switched telephone network via a modem. The internal baud rate generator can be programmed tosame time one is being read by the processor.
But I don’t like it. 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. The eight bits of the read- only status register are depicted in table xcia and serve to indicate the status of both the transmitter and receiver portions of the ACIA at any instant. Operation of the ACIA The software model of the has four user- accessible registers as defined in table 1.
That is, all the engineer needs to understand about the ACIA is the nature of its aca and receiver- side interfaces. You can load CRA with 0A 16 to disable both channels during zcia 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.
It is not possible to provide a full input routine here, as 66850 a routine would include recovery procedures from the errors detected by the ACIA. Consequently, connecting one serial link with another may be difficult because so many options are available. As there are four registers and yet the ACIA has only a single register select input, RS, a way must be found to distinguish between registers.
6850 ACIA chip
An asynchronous serial data link is character orientedbecause information is transmitted in the form of groups of bits called characters. Serial data transmission systems have been around for a long time and are found in the telephone human speechMorse code, semaphore and even the smoke signals once used by Native Aia.
At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit. Note that CR7 is a composite interrupt enable bit and enables all the three forms of receiver interrupt described above.
When a 685 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. Qcia latter mode results if the internal baud rate generator is selected for receiver.
From the designer’s point of view, the ‘s hardware can be subdivided acja three sections: When both these bits are high, a break is transmitted by the transmitter data output pin. Many modern ACIAs include on- chip receiver and transmitter clocks, relieving the system designer of the necessity of providing an additional external oscillator. And this is before we consider that there are about seven commonly used values of T, the element duration.