
CPU32+
MC68360 USER’S MANUAL
5.6.2.7.1 CPU Serial Logic. CPU32+ serial logic, shown in the left-hand portion of
Figure 5-22, consists of transmit and receive shift registers and of control logic that includes syn-
chronization, serial clock generation circuitry, and a received bit counter.
Both DSCLK and DSI are synchronized to on-chip clocks, thereby minimizing the chance of
propagating metastable states into the serial state machine. Data is sampled during the high
phase of CLKOUT. At the falling edge of CLKOUT, the sampled value is made available to
internal logic. If there is no synchronization between CPU32+ and development system
hardware, the minimum hold time on DSI with respect to DSCLK is one full period of CLK-
OUT.
Figure 5-22. Debug Serial I/O Block Diagram
The serial state machine begins a sequence of events based on the rising edge of the syn-
chronized DSCLK (see
Figure 5-23). Synchronized serial data is transferred to the input shift
register, and the received bit counter is decremented. One-half clock period later, the output
shift register is updated, bringing the next output bit to the DSO signal. DSO changes rela-
tive to the rising edge of DSCLK and does not necessarily remain stable until the falling edge
of DSCLK.
One clock period after the synchronized DSCLK has been seen internally, the updated
counter value is checked. If the counter has reached zero, the receive data latch is updated
from the input shift register. At this same time, the output shift register is reloaded with the
CONTROL
LOGIC
SERIAL IN
PARALLEL OUT
PARALLEL IN
SERIAL OUT
EXECUTION
UNIT
STATUS
SYNCHRONIZE
MICROSEQUENCER
PARALLEL IN
SERIAL OUT
SERIAL IN
PARALLEL OUT
RESULT LATCH
CONTROL
LOGIC
STATUS
DATA
DSI
DSO
DSCLK
SERIAL
CLOCK
16
RCV DATA LATCH
CPU
INSTRUCTION
REGISTER BUS
16
COMMAND LATCH
DATA
16
DEVELOPMENT SYSTEM
0
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.