3.7 System Reset
The following information is a concise reference only. System reset is a complex op-
eration. To understand operation during and after reset, refer to SECTION 4 SYSTEM
INTEGRATION MODULE, paragraph 4.6 Reset for a more complete discussion of the
reset function.
3.7.1 SIM Reset Mode Selection
The logic states of certain data bus pins during reset determine SIM operating config-
uration. In addition, the state of the MODCLK pin determines system clock source and
the state of the BKPT pin determines what happens during subsequent breakpoint as-
sertions. Table 3-6 is a summary of reset mode selection options.
Table 3-6 SIM Reset Mode Selection
Mode Select Pin
Default Function
(Pin Left High)
CSBOOT 16-Bit
Alternate Function
(Pin Pulled Low)
CSBOOT 8-Bit
DATA0
DATA1
CS0
CS1
CS2
BRBG
BGACK
3
DATA2
CS3
CS4
CS5
FC0FC1FC2
DATA3
DATA4
DATA5
DATA6
DATA7
CS6
ADDR19
CS[7:6]
CS[8:6]
CS[9:6]
CS[10:6]
ADDR[20:19]
ADDR[21:19]
ADDR[22:19]
ADDR[23:19]
DATA8
DSACK0, DSACK1,
AVEC, DS, AS,
SIZ[1:0]
PORTE
DATA9
DATA11
MODCLK
BKPT
IRQ[7:1], MODCLK
Test Mode Disabled
PORTF
Test Mode Enabled
VCO = System Clock
Background Mode Disabled
EXTAL = System Clock
Background Mode Enabled
MOTOROLA
3-16
OVERVIEW
MC68331
USER’S MANUAL
MOTOROLA [ MOTOROLA ]
