
Chapter 21 External Bus Interface (S12XEBIV2)
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
789
Table 21-1. External System Signals Associated with XEBI
Signal
I1/O
1 All inputs are capable of reducing input threshold level
EBI Signal
Multiplex
(T)ime2
(F)unction3
2 Time-multiplex means that the respective signals share the same pin on chip level and are active alternating in a dedicated
time slot (in modes where applicable).
3 Function-multiplex means that one of the respective signals sharing the same pin on chip level continuously uses the pin
depending on conguration and reset state.
Description
Available in Modes
NS
SS
NX
ES
EX
ST
RE
O
—
Read Enable, indicates external read access
No
Yes
No
ADDR[22:20]
O
T
—
External address
No
Yes
ACC[2:0]
O
—
Access source
No
Yes
ADDR[19:16]
O
T
—
External address
No
Yes
IQSTAT[3:0]
O
—
Instruction Queue Status
No
Yes
ADDR[15:1]
O
T
—
External address
No
Yes
IVD[15:1]
O
—
Internal visibility read data (IVIS = 1)
No
Yes
ADDR0
O
T
F
External address
No
Yes
IVD0
O
Internal visibility read data (IVIS = 1)
No
Yes
UDS
O
—
Upper Data Select, indicates external access
to the high byte DATA[15:8]
No
Yes
No
LSTRB
O
—
F
Low Strobe, indicates valid data on DATA[7:0]
No
Yes
LDS
O
—
Lower Data Select, indicates external access
to the low byte DATA[7:0]
No
Yes
No
R/W
O
—
F
Read/Write, indicates the direction of internal
data transfers
No
Yes
WE
O
—
Write Enable, indicates external write access
No
Yes
No
DATA[15:8]
I/O
—
Bidirectional data (even address)
No
Yes
DATA[7:0]
I/O
—
Bidirectional data (odd address)
No
Yes
EWAIT
I
—
External control for external bus access
stretches (adding wait states)
No
Yes
No
Yes
No