16-07-2013, 04:12 PM
Interfacing chips
[attachment=56636]
Programmable Communication Interface – PCI (8251)
Programmable Interval Timer (8253)
Programmable Peripheral Interfacing - PPI (8255)
Programmable DMA controller (8257)
Programmable Interrupt Controller (8259)
Programmable Keyboard Display Interface (8279)
Synchronous Vs Asynchronous
Asynchronous transfer does not require clock signal.
However, it transfers extra bits(start bits and stop bits) during data communication.
Synchronous does not transfer extra bits. However, it requires clock signal.
8251 USART
The 8251 USART (Universal Synchronous Asynchronous Receiver Transmitter) is capable of implementing either an asynchronous or synchronous serial data communication.
As a peripheral device of a microcomputer system, the 8251 receives parallel data from the CPU and transmits serial data after conversion.
This device also receives serial data from the outside and transmits parallel data to the CPU after conversion.
Pin Description
TXD - This is an output terminal for transmitting data from which serial-converted data is sent out.
TXRDY - This is an output terminal which indicates that the 8251 is ready to accept a transmitted data character.
TXEMPTY - This is an output terminal which indicates that the 8251 has transmitted all the characters and had no data character.
TXC - This is a clock input signal (Active Low) which determines the transfer speed of transmitted data.
In "synchronous mode," the baud rate will be the same as the frequency of TXC. In "asynchronous mode", it is possible to select the baud rate factor by mode instruction. It can be 1, 1/16 or 1/64 the TXC.
Counter Features
Each counter is identical, and each consists of a 16-bit, pre-settable, down counter.
Each is fully independent and can be easily read by the CPU.
When the counter is read, the data within the counter will not be disturbed.
This allows the system or your own program to monitor the counter's value at any time, without disrupting the overall function of the 8253.
[attachment=56636]
Programmable Communication Interface – PCI (8251)
Programmable Interval Timer (8253)
Programmable Peripheral Interfacing - PPI (8255)
Programmable DMA controller (8257)
Programmable Interrupt Controller (8259)
Programmable Keyboard Display Interface (8279)
Synchronous Vs Asynchronous
Asynchronous transfer does not require clock signal.
However, it transfers extra bits(start bits and stop bits) during data communication.
Synchronous does not transfer extra bits. However, it requires clock signal.
8251 USART
The 8251 USART (Universal Synchronous Asynchronous Receiver Transmitter) is capable of implementing either an asynchronous or synchronous serial data communication.
As a peripheral device of a microcomputer system, the 8251 receives parallel data from the CPU and transmits serial data after conversion.
This device also receives serial data from the outside and transmits parallel data to the CPU after conversion.
Pin Description
TXD - This is an output terminal for transmitting data from which serial-converted data is sent out.
TXRDY - This is an output terminal which indicates that the 8251 is ready to accept a transmitted data character.
TXEMPTY - This is an output terminal which indicates that the 8251 has transmitted all the characters and had no data character.
TXC - This is a clock input signal (Active Low) which determines the transfer speed of transmitted data.
In "synchronous mode," the baud rate will be the same as the frequency of TXC. In "asynchronous mode", it is possible to select the baud rate factor by mode instruction. It can be 1, 1/16 or 1/64 the TXC.
Counter Features
Each counter is identical, and each consists of a 16-bit, pre-settable, down counter.
Each is fully independent and can be easily read by the CPU.
When the counter is read, the data within the counter will not be disturbed.
This allows the system or your own program to monitor the counter's value at any time, without disrupting the overall function of the 8253.