Synchronous Mode Transmission

SILICON GATE MOS 8251

Synchronous Mode (Transmission)

The TxD output is continuously high until the CPU sends its first character to the 8251 which usually is a SYNC character. When the CTS line goes low, the first character is serially transmitted out. All characters are shifted out on the falling edge of TxC. Data is shifted out at the same rate as the TxC.

Once transmission has started, the data stream at TxD out- put must continue at the TxC rate. If the CPU does not pro- vide the 8251 with a character before the 8251 becomes empty, the SYNC characters (or character if in single SYNC word mode) will be automatically inserted in the TxD data stream. In this case, the TxEMPTY pin is raised high to sig- nal that the 8251 is empty and SYNC characters are being sent out. The TxEMPTY pin is internally reset by the next character bei ng written into the 8251.

Synchronous Mode (Receive)

In this mode, character synchronization can be internally or externally achieved. If the internal SYNC mode has been programmed, the receiver starts in a HUNT mode. Data on the Rx.D pin is then sampled in on the rising edge of RxC. The content of the Rx buffer is continuously compared with the first SYNC character until a match occurs. If the 8251 has been programmed for two SYNC characters, the subsequent received character is also compared; when both SYNC characters have been detected, the USART ends the HUNT mode and is in character synchronization. The SYN- DET pin is then set high, and is reset automatically by a

STATUS READ.

In the external SYNC mode, synchronization is achieved by applying a high level on the SYNDET pin. The high level can be removed after one RxC cycle.

Parity error and overrun error are both checked in the same way as in the Asynchronous Rx mode.

The CPU can command the receiver to enter the HUNT mode if synchronization is lost.

	CHARACTER LENGTH
	o	1	0
	o	0	1	1
	5	6	7	8
	BITS	BITS	BITS	BITS
L.....-	- ..PARITY ENABLE
	(1 = ENABLE)
	(0 = DISABLE)
L.....-	.. EVEN PARITY GENERATION/CHECK
	1 c EVEN
	0=000

'" ----------- ..EXTERNAL SYNC DETECT

1 = SYNDET IS AN INPUT o= SYNDET IS AN OUTPUT

" -------------.... SINGLE CHARACTER SYNC

1 = SINGLE SYNC CHARACTER

0= DOUBLE SYNC CHARACTER

Mode Instruction Format, Synchronous Mode

CPU BYTES (5-8 BITS/CHAR)

DATA C~~RACTERS

ASSEMBLED SERIAL DATA OUTPUT (TxD)

DATACHA~~AC_T_E_RS ~

RECEIVE FORMAT

SERIAL DATA INPUT (RxD)

DATACHAR~~C_TE_R_S ___

CPU BYTES (5-8 BITS/CHAR)

DATA CH:~ACTERS

Synchronous Mode, Transmission Format

5-141

8080 specifications

The Intel 8085 and 8080 microprocessors were groundbreaking innovations in the world of computing, paving the way for future microprocessor development and personal computing.

The Intel 8080, introduced in 1974, was an 8-bit microprocessor that played a fundamental role in the early days of personal computing. With a 16-bit address bus, it had the capability to address 64 KB of memory. Running at clock speeds of 2 MHz, the 8080 was notable for its instruction set, which included 78 instructions and 246 opcodes. It supported a range of addressing modes including direct, indirect, and register addressing. The 8080 was compatible with a variety of peripherals and played a crucial role in the development of many early computers.

The microprocessor's architecture was based on a simple and efficient design, making it accessible for hobbyists and engineers alike. It included an 8-bit accumulator, which allowed for data manipulation and storage during processing. Additionally, the 8080 featured registers like the program counter and stack pointer, which facilitated program flow control and data management. Its ability to handle interrupts also made it suitable for multitasking applications.

The Intel 8085, introduced in 1976, was an enhancement of the 8080 microprocessor. It maintained a similar architecture but included several key improvements. Notably, the 8085 had a built-in clock oscillator, simplifying system design by eliminating the need for external clock circuitry. It also featured a 5-bit control signal for status line management, which allowed for more flexible interfacing with peripheral devices. The 8085 was capable of running at speeds of up to 3 MHz and had an extended instruction set with 74 instructions.

One of the standout features of the 8085 was its support for 5 extra instructions for stack manipulation and I/O operations, which optimized the programming process. Additionally, it supported serial communication, making it suitable for interfacing with external devices. Its 16-bit address bus retained the 64 KB memory addressing capability of its predecessor.

Both the 8080 and 8085 microprocessors laid the groundwork for more advanced microprocessors in the years that followed. They demonstrated the potential of integrated circuits in computing and influenced the design and architecture of subsequent Intel microprocessors. Their legacy endures in the way they revolutionized computing, making technology accessible to a broader audience, and their influence is still felt in the design and architecture of modern microprocessors today.

Intel 8080 manual Synchronous Mode Transmission, Synchronous Mode Receive

Models: 8080