User`s manual

Host Computer Hardware

Motorola Functional Description 3-9

Figure 3-7. Fan Out of TCK at Source

Either configuration above is equally valid. The choice will depend on practical

considerations related to each project, or a combination could be used.

JTAG signal TMS may also need some consideration. Although TMS is not subject to the

strict requirements as TCK, it is still important that TMS has settled to a valid level at the

rising edge of TCK.

3.1.8 Resetting Target DSP Devices.

The RESET signal and TRST signals from the command converter are typically connected

to all target devices on a JTAG chain. R

ESET and TRST are asserted by the ADS

command FORCE R. All devices on the JTAG chain handling the specified command

converter device are reset. Execution control is established immediately after deassertion

of TRST before any instructions are executed. The sequence of events is illustrated in

Figure 3-8. Because all targets on the JTAG chain are connected to the same RESET

signal, all devices enter reset. The JTAG controller is still active after deassertion of TRST

during reset, and while RESET

is held low, the JTAG instruction DEBUG_REQ is

clocked in. When RESET

is deasserted, the device is immediately in Debug mode, with no

instructions executed since releasing RESET

Figure 3-8. Reset JTAG Device with RESET Signal

TCK TCK TCK TCK

TCK TCK TCK

TCK TCK TCK TCK

TCK TCK

TCK

AA1951

RESET

INSTRUCTION

DEBUG_REQ

COMMAND CONVERTER

ASSERTS RESET

. ALL

TARGETS ENTER RESET.

JTAG INSTRUCTION

DEBUG_REQUEST IS

LOADED.

COMMAND CONVERTER

RELEASES RESET

. TARGETS

EXIT RESET IN DEBUG MODE

AA1969

TRST

JTAG RESET