During initialization, D5H, A4H, LXI Sp

During initialization:
MVI	A, D5H	SET TIMER COUNT TO 5550* FOR REFRESH COUNT
OUT	TIMER MSBYTE
MVI	A, A4H	INTERRUPT CPU AT TO (TIMER OUT)
OUT	TIMER LSBYTE
MVI	A, COH	START COUNTER, PLACE CO IN 8155 STATUS REG.
OUT	TIMER COMMAND

Program
AT RST 7.5 RETURN ADDRESS			CALL RFRS	(REFRESH SERVICE)
TOTAL	#CYCLES
CYCLES
	10	RFRS:	LXIHL,O	SAVE STACK POINTER IN HL
	10		DADSP
30	10		LXI Sp, 0080	32K - 48K REFRESH
	10		POP BC
	10		POP BC	REFRESH, DUMMY READ
				64 TIMES
	6		SPHL	RESTORE STACK POINTER
	4		EI	ENABLE INTERRUPTS
20	10		RET	RETURN
690	TOTAL CYCLES		(round up to 700)

*6,250 available cycles - 700 to do refresh. Counter should count 5550 =15A4H for 8085A; for 8085A-2 must count 10,000-700 = 9300 = 2454H. To set counter to automatic reload, most significant bits in timer of 8155 must be set to 1. Therefore, for 808SA use D5A4H and for 8085A-2 use E454H.

Figure 11. Software Refresh

11.

\'11

The standard technique for interfacing the 8085A proc- essor to the 8237 DMA controller is shown in the MCS·85 User'sManual and is reproduced in Figure 12. This configuration is set up to interface with standard memories or peripherals; i.e., one~ that don'tshare their data bus with addresses, not the MCS-85 family com· ponents (8155, 8355, 8755A, etc.). DMA is unlikely with these MCS·85 components as they are intended for

minimum system applications. If the system has both MCS·85and standard addressed components, and DMA is used for the standard addressed components, ALE must be or'ed with ADSTB from the 8257. This is necessary to deselect the MCS-85 components from the bus. Due to the latching feature of the MCS·85 com· ponents, bus contention may result if this is not done and DMA tries to use the bus.

A1·14

MCS-80/85 specifications

The Intel MCS-80/85 family, introduced in the late 1970s, is a seminal collection of microprocessors that played a pivotal role in the early days of computing. The MCS-80 series, initially targeting embedded systems and control applications, gained remarkable attention due to its innovative architecture and flexible programming capabilities.

The MCS-80 family is anchored by the 8080 microprocessor, which was one of the first fully integrated 8-bit microprocessors. Released in 1974, the 8080 operated at clock speeds ranging from 2 MHz to 3 MHz and featured a 16-bit address bus capable of addressing up to 64KB of memory. The processor’s instruction set included around 78 instructions, providing extensive capabilities for data manipulation, logic operations, and branching.

Complementing the 8080 was a suite of support chips, forming the MCS-80 platform. The most notable among them was the 8155, which integrated a static RAM, I/O ports, and a timer, tailored for ease of designing systems around the 8080. Other support chips included the 8085, which provided improvements with an integrated clock generator, making it compatible with more modern designs and applications.

The MCS-85 series, on the other hand, revolves around the 8085 microprocessor, which provided a more advanced architecture. The 8085 operated at clock speeds of up to 6 MHz and came with a 16-bit address bus, similar to its predecessor. However, it introduced more sophisticated features, including an enhanced instruction set and support for interrupt-driven programming. These enhancements made the 8085 especially appealing to developers working in real-time processing environments.

The MCS-80/85 family utilized NMOS technology, known for its lower power consumption and higher performance compared to previous technologies like TTL. The family’s architecture allowed for easy interfacing with a variety of peripherals, making it a favorite for educational institutions and hobbyists embarking on computer engineering projects.

With its robustness, versatility, and affordability, the Intel MCS-80/85 microprocessors laid the groundwork for many subsequent microcomputer systems and applications. The legacy of this powerful family continues to influence modern microprocessor design, emphasizing the importance of reliable architecture in a rapidly evolving technology landscape.

Intel MCS-80/85 manual During initialization, D5H, A4H, LXI Sp, Round up to

Models: MCS-80/85