AN2408 Freescale Semiconductor / Motorola, AN2408 Datasheet - Page 3

• Manufacturer Part Number: AN2408
• Description: Examples of HCS12 External Bus Design A Companion Note to AN2287/D
• Manufacturer: Freescale Semiconductor / Motorola

Figure 2
to the external memory space configured in narrow mode. Notice that the MCU automatically breaks the
write into two appropriate byte accesses and that the R/W signal is not negated.
Freescale Semiconductor
PB0
PB1
PB2
PB3
PB4
PB5
PB6
PB7
PA0
PA1
PA2
PA3
PA4
PA5
PA6
PA7
PE4
PE2
MCU ADDR[0]
MCU ADDR[1]
MCU ADDR[2]
MCU ADDR[3]
MCU ADDR[4]
MCU ADDR[5]
MCU ADDR[6]
MCU ADDR[7]
MCU ADDR[8]
MCU ADDR[9]
MCU ADDR[10]
MCU ADDR[11]
MCU ADDR[12]
MCU ADDR[13]
MCU ADDR[14]
MCU ADDR[15]
MCU ECLK
MCU R/W
is a logic analyzer trace showing the narrow mode access. It was generated by a word access
Figure 1. Byte-Wide SRAM Interface (Narrow Mode) ECLK Gated
4
5
U4B
74FCT00
6
Examples of HCS12 External Bus Design, Rev. 2
13
14
17
18
11
3
4
7
8
1
U2
74FCT374
D0
D1
D2
D3
D4
D5
D6
D7
LE
OE
10
Example #1 — Byte-Wide SRAM Interface (Narrow Mode) ECLK Gated
1
2
9
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
U4A
74FCT00
U4C
74FCT00
2
5
6
9
12
15
16
19
3
8
2
3
1
U3A
74FCT139
A
B
G
WE*
OE*
Y 0
Y 1
Y 2
Y 3
4
5
6
7
10
25
24
21
23
22
27
20
26
9
8
7
6
5
4
3
2
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
OE
WE
CS1
CS2
U1
6264/S0
D0
D1
D2
D3
D4
D5
D6
D7
11
12
13
15
16
17
18
19
DATA[0]
DATA[1]
DATA[2]
DATA[3]
DATA[5]
DATA[4]
DATA[6]
DATA[7]
PA0
PA1
PA2
PA3
PA4
PA5
PA6
PA7
3