1 Introduction

The UCD90xxx family of digital sequencers, also known as system health monitors, are flexible and powerful enough to meet user sequencing, monitoring, margining and other needs. The entire families of devices are designed to have similar behaviors, but with a different number of rails or some other minor features. Users only need to learn how to use the device once, and can then seamlessly switch to other devices within the family that best fit their future designs. This document is to help applications to access GPIOs from the devices. This document does not apply to the UCD9080 and UCD9081 devices. All commands listed in the document can be found in the publications listed in Section 5.

All byte values are represented in hexadecimal format. These are the codes to understand all I²C communications that occur:

• [St] - This is the I²C Start bit.
• [Sr] - This is the I²C Restart bit. It is identical to the Start bit.
• [Sp] - This is the I²C Stop bit.
• [A] - This is the I²C Acknowledge bit.
• [N] - This is I²C No Acknowledge bit or NACK.
• [AddrW] - This is the I²C device address with the Write bit.
• [AddrR] - This is the I²C device address with the Read bit.
• [W:x55] - This is an example of a write byte for value 55 hexadecimal.
• [W/R:Data_ⁿ] - This is to indicate that a byte is being write/read by the I²C master. The n subscript is an ordered integer use to distinguish multiple bytes read back. Data_1 is the MSB, and Data_2 is the LSB for two bytes read.