GDC21D601 Datasheet, PDF (167/189 Pages) Hynix Semiconductor – 32-Bit RISC MCU

GDC21D601
3.1 Reset
The boundary-scan interface includes a state-machine controller (the TAP controller).
A pulldown resistor is included in the nTRST pad which holds the TAP controller state machine in a safe state
after power up. In order to use the boundary scan interface, nTRST should be driven HIGH to take the TAP state
machine out of reset.
The action of reset (either a pulse or a DC level) is as follows:
* System mode is selected (i.e. the boundary scan chain does NOT intercept any of the signals passing between
the pads and the core).
* IDcode mode is selected. If TCK is pulsed, the contents of the ID register will be clocked out of TDO.
Note : The TAP controller inside ARM7201 contains a scan chip register which is reset to the value b0011 thus
selecting the boundary scan chain. If this register is programmed to any value other than b0011, then it
must be reprogrammed with b0011 or a reset applied before boundary scan operation can be attempted.
3.2 Pullup Resistors
The IEEE 1149.1 standard requires pullup resistors in the input pins. However, to ensure safe operation an internal
pulldown is present in the nTRST pin and therefore will have to be driven HIGH when using this interface.
Table 1. Internal Resistors for Input Pins
PIN
TCLK
nTRST
TMS
TDI
INTERNAL RESISTOR
Pullup
Pulldown
Pullup
Pullup
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