IOH1 and IIL Specifications Explanation

What are the IOH1 and IIL1 DC characteristics? Why should systems be designed to meet them? The data sheets currently provide an ambiguous explanation to these questions.

The IOH1 and IIL1 are provided in most of the MCS-96 device family data sheets. Although the pins that the specifications refer to vary for the different devices, the purpose of these specifications is the same for all the devices. See the current data sheets for the MCS-96 device for these specification values. Also the data sheets list which pins these specifications cover for each device. For example, IOH1 and IIL1 specifications are for pin P2.0 on the 8XC196KC device.

The IOH1 specification is the logical 1 output current in reset on the specified pins. If this current is exceeded, the device can inadvertently be placed into a test mode. The IIL1 specification is the logical 0 input current in reset on the specified pins. This specification must be met for the device to successfully enter a test mode, such as ONCE mode.

The IOH1 specification characterizes the amount of current the device sources with a logical 1 input voltage on the specified pin. The external circuitry should not sink more than the specified current level. If this specification is not met, the voltage on the pin can be lowered below the input high level.

The IIL1 specification characterizes the minimum current the external circuit must sink with a logical 0 voltage on the specified pin. The external circuitry should be able to sink the maximum current shown in the data sheet to ensure the device enters the desired test mode. If the specification is not met, the voltage on the pin may not be pulled to the input low voltage.