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METHOD AND APPARATUS TO DRIVE UNIMPLEMENTED INPUT PINS IN A DATA PROCESSING SYSTEM

IP.com Disclosure Number: IPCOM000007314D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-14
Document File: 6 page(s) / 304K

Publishing Venue

Motorola

Related People

Oded Yishay: AUTHOR [+3]

Abstract

The Motorola Modular Family (MMF) is currently composed of two groups of products; the MC68HCl6 family, based on the CPU16 core, and the MC68HC300 family, based on the CPU32 core. Each product in the MMF contains a CPU module, a system integration module, and one or more of the other modules available in this family, A new Module, the "GRIM" is targeted for a broad range of modular MCU applications. It has a minimum number of pins required for basic opera- tion and test. It also has a set of optional pins to support incremental features, without the need to re-design the GRIM module.

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MOTOROLA Technical Developments Volume 23 October 1994

METHOD AND APPARATUS TO DRIVE UNIMPLEMENTED INPUT PINS IN A DATA PROCESSING SYSTEM

by Oded Yishay, Jeffrey Dale Quinn and Kenneth Leo McIntyre Jr.

THE PROBLEM

  The Motorola Modular Family (MMF) is currently composed of two groups of products; the MC68HCl6 family, based on the CPU16 core, and the MC68HC300 family, based on the CPU32 core. Each product in the MMF contains a CPU module, a system integration module, and one or more of the other modules available in this family,

A new Module, the "GRIM" is targeted for a broad range of modular MCU applications. It has a

minimum number of pins required for basic opera- tion and test. It also has a set of optional pins to support incremental features, without the need to re-design the GRIM module.

  To support the optional pin set, internal logic was added, associated with each pin. This circuit is always there, and may be used even if the pin is unimplemented. This circuit must also be tested.

  Optional pins in Port F of the GRIM have the same problem; An edge detect circuit detects any edge on port F signals, and may generate an inter- rupt ifenabled to detect that edge.

  The edge detect should work on both input or output pins. Input pins are driven by external logic, while the Output pins are driven by the GRIM itself As mentioned before, it is required to detect the edge regardless ifthe pin is input or output.

  Traditionally, unimplemented input pins are permanently tied off to a fixed logic level, high or low. The level will usually be the inactive state.

  Another tie-off method would be to connect the output of the circuit of the unimplemented pin to the input going back to the circuit. However, this solution imposes different behavior of the circuit if the pin is available, or ifthe pin is unavailable.

0 Motorola, Inc. ,994

  For example, when a pin is configured as an input, in case that the pin is implemented, the input is driven by the external logic. If the pin is unimplemented it will be connected to the output from the circuit. In the case of the unimplemented pin, an edge on this output will activate the edge detect circuit. In the case that the pin is implemented, it will not detect any edge. This also causes signih- cant test problems.

THE SHOW IRQ PROBLEM:

  Show IRQ Signals are internal IMB signals driven out on the external IRQ pins. Port-F IRQ visibility in the Port F Pin Data Register is in addition to the signals being driven onto the external pins.

  This visibility is required even if the external pins are not present on the device containing the GRIM. Therefore, the Pin Data Register must have an optional feedback path for the Show IRQ Sig- nals. In this case the Show IRQ test vectors can also be reused, even ifthe pins are unimplemented. How- ever, it is required to avoid any different behavior if the pin is implemented or not.

Figure 1 -The Traditional way-optional pin:

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