eZ80L92 MCU
Product Specification
162
ZDI Data Out
(Read)
ZDI Data Out
(Read)
ZCL
ZDA
Start Signal
Figure 38. ZDI Read Timing
ZDI Single-Bit Byte Separator
Following each 8-bit ZDI data transfer, a single-bit byte separator is used. To initiate a
new ZDI command, the single-bit byte separator must be High (logical 1) to allow for a
new ZDI START command to be sent. For all other cases, the single-bit byte separator can
be either Low (logical 0) or High (logical 1). When ZDI is configured to allow the CPU to
accept external bus requests, the single-bit byte separator should be Low (logical 0) during
all ZDI commands. This Low value indicates that ZDI is still operating and is not ready to
relinquish the Bus. The CPU does not accept the external bus requests until the single-bit
byte separator is a High (logical 1). For more information about accepting bus requests in
ZDI DEBUG mode, please see the Bus Requests During ZDI Debug Mode section on
page 166.
ZDI Register Addressing
Following a START signal the ZDI master must output the ZDI register address. All data
transfers with the ZDI block use special ZDI registers. The ZDI control registers that
reside in the ZDI register address space should not be confused with the eZ80L92 periph-
eral registers that reside in the I/O address space.
Many locations in the ZDI control register address space are shared by two registers, one
for Read-Only access and one for Write-Only access. As an example, a Read from ZDI
®
register address 00h returns the eZ80 Product ID Low Byte while a Write to this same
location, 00h, stores the Low byte of one of the address match values used for generating
break points.
The format for a ZDI address is seven bits of address, followed by one bit for Read or
Write control, and completed by a single-bit byte separator. The ZDI executes a Read or
Write operation depending on the state of the R/W bit (0 = Write, 1 = Read). If no new
PS013012-1004
P R E L I M I N A R Y
ZiLOG Debug Interface
ZILOG [ ZILOG, INC. ]
