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Chapter 18 External Bus Interface (S12XEBIV4)
MC9S12XF - Family Reference Manual, Rev.1.19
820
Freescale Semiconductor
Table 18-2. EBICTL0 Field Descriptions
Field
Description
7
ITHRS
Reduced Input Threshold — This bit selects reduced input threshold on external data bus pins and specic
control input signals which are in use with the external bus interface in order to adapt to external devices with a
3.3 V, 5 V tolerant I/O.
The reduced input threshold level takes effect depending on ITHRS, the operating mode and the related enable
signals of the EBI pin function as summarized in
Table 18-3.0 Input threshold is at standard level on all pins
1 Reduced input threshold level enabled on pins in use with the external bus interface
5
HDBE
High Data Byte Enable — This bit enables the higher half of the 16-bit data bus. If disabled, only the lower 8-
bit data bus can be used with the external bus interface. In this case the unused data pins and the data select
signals (UDS and LDS) are free to be used for alternative functions.
0 DATA[15:8], UDS, and LDS disabled
1 DATA[15:8], UDS, and LDS enabled
4–0
ASIZ[4:0]
External Address Bus Size — These bits allow scalability of the external address bus. The programmed value
corresponds to the number of available low-aligned address lines (refer to
Table 18-4). All address lines
ADDR[22:0] start up as outputs after reset in expanded modes. This needs to be taken into consideration when
using alternative functions on relevant pins in applications which utilize a reduced external address bus.
Table 18-3. Input Threshold Levels on External Signals
ITHRS
External Signal
NS
SS
NX
ES
EX
ST
0
DATA[15:8]
TAGHI, TAGLO
Standard
Reduced
Standard
DATA[7:0]
EWAIT
Standard
1
DATA[15:8]
TAGHI, TAGLO
Standard
Reduced
if HDBE = 1
Reduced
DATA[7:0]
Reduced
EWAIT
Reduced
if EWAIT
enabled(1)
1. EWAIT function is enabled if at least one CSx line is congured respectively in MMCCTL0. Refer to S12X_MMC section and
Standard
Reduced
if EWAIT
Standard
Table 18-4. External Address Bus Size
ASIZ[4:0]
Available External Address Lines
00000
None
00001
UDS
00010
ADDR1, UDS
00011
ADDR[2:1], UDS
::
10110
ADDR[21:1], UDS