mc68336 Freescale Semiconductor, Inc, mc68336 Datasheet - Page 51

• Manufacturer Part Number: mc68336
• Description: An Introduction To The Mc68331 And Mc68332
• Manufacturer: Freescale Semiconductor, Inc

After the double bus fault occurs, the MCU drives the HALT line low and can only be restarted by a reset.
When the HALT line is driven low internally, the double bus fault monitor will immediately cause a reset if it
is enabled. If the double bus fault monitor has been disabled by clearing the HME bit in the system protec-
tion control register (SYPCR), the MCU will remain halted indefinitely and must be reset externally.
5.2.8 Problem: A Chip-Select Generates the Wrong Number of Wait States
MC68331/332
M68331/332TUT/D
3. When a bus error occurs while the CPU is loading information from a bus error stack frame during
1. Either DSACK1 or DSACK0 has floated low. These signals should be tied high via a pull-up resistor
2. Multiple chip-selects with different wait states are responding to the same address (it does not matter
3. The MCU sees only base addresses that lie on a word boundary of the block size. It will interpret each
execution of a return from exception (RTE) instruction.
or be configured as I/O pins. The DSACK pins, along with other bus control signals, are configured
as I/O pins by driving DATA8 low during reset or by programming the appropriate CSPAR bits.
whether the chip-select pins are connected to anything). Whether or not multiple chip-selects re-
spond to the same address is determined by both the base address and the block size in the asso-
ciated chip-select base address register (CSBAR).
base address as an address that is on a word boundary. This will cause an incorrectly programmed
chip-select circuit to match on an unexpected address. An example of how to determine if chip-select
circuits are programmed correctly is shown below.
A. On a sheet of paper, make a table with four columns as shown in Table 8. Initialize the base ad-
B. Compare the base address register values to see if any overlap. In addition to checking the actual
dress and option registers, then look at all of the base address and option registers. Fill in the ap-
propriate cell in the table with the value in the corresponding option register and base address
register. In addition, fill in the BLKSZ cell with the block size indicated by the last three bits of the
base address register. Table 9 shows block size values.
values in the registers, check the block sizes and thus the number of address lines compared.
Since the MCU does not look at all 24 address lines when it compares for a match, two chip-select
circuits can respond to the same base address, even though the base address registers contain
different values.
BLKSZ[2:0]
CSBOOT
CS10
CS0
CS1
CS
000
001
010
011
100
101
110
111
Freescale Semiconductor, Inc.
Table 9 Block Size Encodings for Chip-Selects
.
.
.
For More Information On This Product,
Table 8 Sample Chip-Select Values
Go to: www.freescale.com
CSBARx
Block Size
128 Kbyte
256 Kbyte
512 Kbyte
$0003
$0504
$1002
$0400
16 Kbyte
64 Kbyte
1 Mbyte
2 Kbyte
8 Kbyte
.
.
.
CSORx
Address Lines Compared
$68B0
$58FE
$4F3E
$5830
.
.
.
ADDR[23:11]
ADDR[23:13]
ADDR[23:14]
ADDR[23:16]
ADDR[23:17]
ADDR[23:18]
ADDR[23:19]
ADDR[23:20]
BLKSZ
128K
64K
16K
2K
.
.
.
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