ScanWorks^® JTAG Flash Memory Program Generation

Product Overview

Several methods are used to program flash devices after they have been assembled onto a board. Each has advantages and disadvantages, but only on-board programming with JTAG is fast, convenient, and can be used throughout a product’s life cycle. On-board programming with boundary scan enables you to use the same tool to load program data during design verification and debug, during manufacturing tests, and in the field for system upgrades. Programming times can approach theoretical times and file sizes are not the problem they are with other methods.

Flash Memory Programming with JTAG or Boundary Scan

Flash memories have fairly simple algorithms for writing and reading data enabling the algorithm to be emulated by a series of scan operations. These scan operations apply the address and program data to the appropriate pins and toggle the control signals at the appropriate time. This requires the data, address, and control signals to be accessible from a boundary-scan device, the device to be accessible to a boundary-scan tool, and the tool to know the sequence of operations needed to control the flash device.

Several considerations are required when estimating programming times using JTAG (boundary scan):

• Number of scan operations required
• Length of the boundary-scan path
• Maximum TCK supported by the design
• Amount of data to be loaded

The number of scans needed to write data to a flash device depends on the device type. Some require only four scans while other require as many as eight. Controlling the write enable signal by a non-scan signal can reduce the number of scans. Reducing the number of scan required from four to two reduces programming time by approximately 50%. The length of the scan path can be minimized by the selection of the device used for access and by placing all other scan devices in BYPASS. Often there is only one option, allowing no improvements. The maximum TCK supported is the frequency supported by the slowest device in the path, or the maximum frequency supported by the board design. Careful device selection and board design minimizes programming times. The amount of data to be loaded is usually not optional, but by carefully planning the manufacturing flow, you can minimize the impact on manufacturing throughput.

Previous : Next                   Page 1 of 2