MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-5
EXOFF disables the CLKOUT external clock output pin by placing the pin in a high-
impedance state. CLKOUT is enabled at power-up unless explicitly disabled by writing
a zero to EXOFF.
CPUD disables the IPIPE/DSO and IFETCH/DSI instruction tracking pins by placing
them in a high-impedance state when the MCU is not in background debug mode
(BDM). When the MCU enters BDM and FREEZE is asserted, IPIPE/DSO and
IFETCH/DSI become active and serve as the BDM serial I/O lines.
ABD and RWD disable the ADDR[2:0] and R/W pins by placing them in a high-imped-
ance state. These pins should be disabled because they cannot be used for discrete
I/O and have no use in single-chip mode.
4.2.5 Show Internal Cycles
A show cycle allows internal bus transfers to be monitored externally. The SHEN field
in SCIMMCR determines what the external data bus interface does during internal
transfer operations. Table 4-3 shows whether data is driven externally, and whether
external bus arbitration can occur. The external address bus is always driven. Refer to
4.2.6 FREEZE Assertion Response
When the CPU32 enters background debug mode, the IMB FREEZE signal is
asserted. The FRZ[1:0] bits in SCIMMCR control the behavior of the software watch-
dog, periodic interrupt timer, and bus monitor in response to FREEZE assertion. By
default, these protection mechanisms are disabled in BDM; they can be selectively
enabled by the FRZ[1:0] bits as shown in Table 4-4.
Table 4-3 Show Cycle Enable Bits
SHEN[1:0]
Effect
00
Show cycles disabled, external arbitration enabled
01
Show cycles enabled, external arbitration disabled
10
Show cycles enabled, external arbitration enabled
11
Show cycles enabled, external arbitration enabled;
internal activity is halted by a bus grant
Table 4-4 Effects of FREEZE Assertion
FRZ[1:0]
Disabled Elements
00
None
01
Bus monitor
1
0
Software watchdog and periodic interrupt timer
11
Both
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Freescale Semiconductor, Inc.
For More Information On This Product,
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