Spectrum Digital XDS560R Installation Manual page 23

Distributor of Spectrum Digital Inc: Excellent Integrated System Limited
Datasheet of 702570 - TARGET ADAPTER CBL 20P CTI JTAG
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Spectrum Digital, Inc
3.2 Bus Protocol
The IEEE 1149.1 specification covers the requirements for JTAG bus slave devices
(such as the TMS320C5x family) and provides certain rules, summarized as follows:
__ The TMS/TDI inputs are sampled on the rising edge of the TCK signal of the
device.
__ The TDO output is clocked from the falling edge of the TCK signal of the device
When JTAG devices are daisy-chained together, the TDO of one device has
approximately a half TCK cycle set up to the next device's TDI signal. This type of
timing scheme minimizes race conditions that would occur if both TDO and TDI
were timed from the same TCK edge. The penalty for this timing scheme is a
reduced TCK frequency.
The IEEE 1149.1 specification does not provide rules for JTAG bus master
(emulator) devices.
3-4 XDS560R JTAG Emulator Installation Guide