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Intel MCS-80/85 manual ·2Clock Related Timing Vs MHz Considerations

Models: MCS-80/85

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Figure 16. 8085A·2Clock Related Timing

3.125 vs. 5 MHz Considerations

The SOB5A (with maximum internal clock frequency of 3.125 MHz) and SOS5A-2 (5 MHz) have some differences in their bus operation. There are two sets of peripherals that can be used with both the SOS5A and A-2. There are the dedicated peripherals in the MCS-S5 family that directly interface with the S085A, A-2 bus and the standard MCS-BO peripherals that Intel also provides. The standard peripherals that are denoted B25X-5 (also the S251A and B27X peripherals) are peripherals that can be used with an SOS5A or SOS5A-2. In the B085A-2 system a wait state is required for proper I/O operation, but even with this wait state system speed is still 30% higher than the BOS5A without wait states. An example wait state generator for this purpose is shown at the end of the peripheral compatibility section in this Application Note (Figure 19).

The main timing differences to consider when using an SOB5A vs. an A-2 are listed in Table 1.

Cycle dependent timings are listed in Table 2. These are very useful when the user is not operating at the full bus speed. Remember that each SOS5A, A-2 device divides its clock input frequency by 2. Therefore, a 10 MHz crystal will produce a 200ns output cycle (denoted as T in the cycle dependent timings). A timing diagram showing the relationships of the timing parameters given in Table 2 can be found on the data sheets.

-Clock (crystal) requirements. The BOS5A, A-2 re- quires the following crystal specifications to run at top bus speed:

8085A 6.25 MHz frequency, parallel resonant, fundamental, 10 mwatt drive level, RS < 75 ohms, CL=20·35 pf, and CS < 7 pf.

8085A-2 10 MHz frequency, all other specifications the same as 8085A.

-Memory and Peripheral Compatibility - Discussed in detail in upcoming sections.

-Cycle dependent timings (Table 2)

Table 1. 8085A VS. 8085A-2.

A1-18

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Intel MCS-80/85 manual ·2Clock Related Timing Vs MHz Considerations
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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.