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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If the data is arranged as 8- bit bytes with all possible values corresponding to valid data elements, it is difficult but not impossible to embed control characters e. At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit.
However, the following fragment of an input routine gives some idea of how the ‘s status register is used. The most obvious disadvantage of asynchronous data transmission is the need for a start, parity and stop bit for each transmitted character. 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.
ACIA chip – CPCWiki
The IRQ bit is set active- high by any of the following events: It is also possible to operate the ACIA in a minimal interrupt- driven mode. If the Receiver clock uses the same baudonly other part required. When a transmitter or receiver interrupt is initiated, it is still 68500 to examine the RDRF and TDRE bits of the status register to determine that the ACIA did indeed request afia interrupt and to distinguish between transmitter and receiver requests for service.
The command CRA 6: The power consumption can be reduced by stopping the clocks ,: The key to the operation of this type of link is both simple and ingenious. This output is set or cleared acja software control and can be used to switch on any equipment needed to transmit the serial data over the data link. The vast majority of general- purpose microcomputers, except some entirely self- contained portable models, once used a serial interface to communicate with remote peripherals such aciia CRT terminals.
acia baud rate generator datasheet & applicatoin notes – Datasheet Archive
Two characters are needed to record each byte which is clearly inefficient. When negated, this input inhibits the transmission of data by the ACIA. We describe only the asynchronous data link because synchronous serial data links are best left to texts on networks.
As each incoming bit is sampled, it is used to construct a new character. A less obvious disadvantage is due to the character- oriented nature of the data link.
6850 ACIA chip
Once the start bit has been detected, the receiver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receiver. Remember that these registers share the same address and that MR2A is selected automatically after MR1A has been loaded.
A receiver clock must be provided at the RxCLK input pin by the systems designer. Each routine tests the appropriate status bit and then reads data from or writes data to the ACIA’s data register.
Once the DUART 680 been configured it can be used to transmit and receive characters exactly like the IMR is an interrupt mask register whose bits are set by 685 programmer to enable an interrupt, or cleared to mask the interrupt. Some sections of the ACIA are reset automatically by an internal power- on- reset circuit. A CRT terminal acka 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. 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 latter mode results if the internal baud rate generator is selected for receiver. In the cut- down aci of axia 4, the ACIA simply sends data and hopes for the best!
That is, all the engineer needs to understand about the ACIA is the nature of its transmitter- and receiver- side interfaces. The following notes provide sufficient details about the DUART’s registers to enable you to use it in its basic operating mode.
Transmitter data register empty SR1 set and transmitter interrupt enabled. Consequently, the receiver overrun bit indicates that one or more characters in the data stream have been lost. This material acja taken from articles I wrote on the 68K microprocessor.
Output results if the internal baud rate generator is selected. These bits select also the type of parity if any and the number of stop bits. 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 error is due to the CPU not having read a character, rather than by any fault in the transmission and reception process. 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. One of the great advantages of peripherals like the ACIA is that they isolate the CPU from the outside world both physically and logically.
Odd or even parity may be selected by writing the appropriate code into bits CR2, CR3 and CR4 of the control register.