EZ80F91MCU Datasheet, PDF (312/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
293
ments with each Read. If the ZDI register address reaches the end of the Read
Only ZDI register address space (20h), the address stops incrementing. Figure 59
illustrates the ZDI’s block Read timing.
ZDI Data Bytes
ZCL
7
8
9
1
2
3
7
8
9
1
2
9
ZDA
A0 Read 0/1 D7 D6 D5 D1 D0 0/1
D7
D6 1
msb
of DATA
Byte 1
lsb of
Single-Bit
ZDI Address Byte Separator
lsb
of DATA
Byte 1
msb
of DATA
Byte 2
Single-Bit
Byte Separator
Figure 59. ZDI Block Data Read Timing
Operation of the eZ80F91 Device during ZDI Break Points
If the ZDI forces the CPU to break, only the CPU suspends operation. The system
clock continues to operate and drive other peripherals. Those peripherals that can
operate autonomously from the CPU can continue to operate, if so enabled. For
example, the Watch-Dog Timer and Programmable Reload Timers continue to
count during a ZDI break point.
When using the ZDI interface, any Write or Read operations of peripheral regis-
ters in the I/O address space produces the same effect as Read or Write opera-
tions using the CPU. Because many register Read/Write operations exhibit
secondary effects, such as clearing flags or causing operations to commence, the
effects of the Read/Write operations during a ZDI break must be taken into con-
sideration.
Bus Requests During ZDI Debug Mode
The ZDI block on the eZ80F91 device allows an external device to take control of
the address and data bus while the eZ80F91 device is in DEBUG mode.
ZDI_BUSACK_EN causes ZDI to allow or prevent acknowledgement of bus
requests by external peripherals. The bus acknowledge only occurs at the end of
the current ZDI operation (indicated by a High during the single-bit byte separa-
tor). The default reset condition is for bus acknowledgement to be disabled. To
allow bus acknowledgement, the ZDI_BUSACK_EN must be written.
When an external bus request (BUSREQ pin asserted) is detected, ZDI waits until
completion of the current operation before responding. ZDI acknowledges the bus
request by asserting the bus acknowledge (BUSACK) signal. If the ZDI block is
PS019209-0504
PRELIMINARY
ZiLOG Debug Interface