EZ80F91MCU Datasheet, PDF (331/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
312
OCI Activation
OCI features clock initialization circuitry so that external debug hardware can be
detected during power-up. The external debugger must drive the OCI clock pin
(TCK) Low at least two system clock cycles prior to the end of the RESET to acti-
vate the OCI block. If TCK is High at the end of the RESET, the OCI block shuts
down so that it does not draw power in normal product operation. When the OCI is
shut down, ZDI is enabled directly and can be accessed via the clock (TCK) and
data (TDI) pins. See the ZiLOG Debug Interface section on page 286 for more
information on ZDI.
OCI Interface
There are six dedicated pins on the eZ80F91 for the OCI interface. Four pins—
TCK, TMS, TDI, and TDO—are required for IEEE Standard 1149.1-compliant
JTAG ports. A fifth pin, TRSTn, is optional for IEEE 1149.1 and utilized by the
eZ80F91 device. The TRIGOUT pin provides additional testability features. These
six OCI pins are described in Table 203.
Table 203. OCI Pins
Symbol
TCK
TRSTn
TMS
TDI
Name
Clock.
TAP Reset
Test Mode Select
Data In
Type
Input
Input
Input
Input
(OCI enabled)
I/O
(OCI disabled)
Description
Asynchronous to the primary eZ80F91 system clock.
The TCK period must be at least twice the system
clock period. During RESET, this pin is sampled to
select either OCI or ZDI DEBUG modes. If Low
during RESET, the OCI is enabled. If High during
RESET, the OCI is powered down and ZDI DEBUG
mode is enabled. When ZDI DEBUG mode is active,
this pin is the ZDI clock. On-chip pull-up ensures a
default value of 1 (High).
Active Low asynchronous reset for the Test Access
Port state register. On-chip pull-up ensures a default
value of 1 (High).
This serial test mode input controls JTAG mode
selection. On-chip pull-up ensures a default value of
1 (High). The TMS signal is sampled on the rising
edge of the TCK signal.
Serial test data input. This pin is input-only when the
OCI is enabled. The input data is sampled on the
rising edge of the TCK signal.
When the OCI is disabled, this pin functions as the
ZDA (ZDI Data) I/O pin. NORMAL mode, following
RESET, configures TDI as an input.
PS019209-0504
PRELIMINARY
On-Chip Instrumentation