Application of CPLD

Programmable Package SG-8018CA(SG7050C) 0.67M~170M

RF cable can be customized for other specifications

With the development of large-scale ultra-large-scale programmable logic devices, logic devices are increasingly used in electronic circuit design due to their low price, flexible design, and rich functions. CPLD can comprehensively integrate logic circuit functions, design the smallest unit according to needs, save system resources, and greatly reduce the connection between functional modules and modules on the circuit board. At the same time, the system is modified and upgraded with its flexible design and online upgrade mode, which reduces the modification of the circuit board itself, improves the overall reliability of the system, saves plate making costs and shortens the design cycle.

However, there are still many details to be aware of when using programmable logic devices, especially for electronic circuit designers who are only beginning to apply them. Only by grasping these details can they be successfully designed.

Application basis

The logic device needs to be understood before design. Take the MAX7000 series as an example. The device pin settings are shown in Figure 1. This is an example of applying a CPLD device to the PCI interface logic to implement localized control of the PCI interface chip output and embedded design of some of the functional blocks.

The components remove the required pins from the power supply section, and most of the remaining components are I/O ports, which can be defined as the control pins required by the system. Need to pay attention to several global signal control pins, such as GCLK, OE and other pins can be used for the control of the entire logic device working timing, generally used for global signal connection. At the same time, it should be noted that the four pins of TDI, TMS, TDO and TCK are program download pins related to online programming, and can also be used as general-purpose pins when necessary. The download line of the ALTERA component can be purchased or made by itself, and the data is relatively complete. To achieve online programming, the PCB design of the CPLD component part needs to be noted that several download pins are not floating, and must be pulled up and pulled down. The circuit is shown in Figure 2. This is easy to ignore, and the download software cannot find the underlying device. The instructions are in the document "In-System Programmability".

By installing the corresponding download line driver in the operating system, the programmable control device can be found in its graphical design software, and it can be programmed and debugged online.