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3-32
PORT A CONTROL REGISTER
{PACNTI
15
14
13
12
11
10
1
0
lcAlcAlcAlcAlcA
CA
CA
CA I CA I CA I CA I CA
CA I CA
CA I CA I
PORT A DATA DIRECTION REGISTER
(PADDRI
15
14
13
12
11
10
1
0
IDAIDAIDAIDAj DA
DA
DA
DA
DA
DA
DA
DA
DA
I
DA
DA
I
DA I
PORT A DATA REGISTER
(PADAT)
15
14
13
12
11
10
1
0
I
PA I PA I PA I PA I PA I PA I PA I PA I PA I PA I PA I PA I PA I PA
PA I PA I
PORT 8 CONTROL REGISTER
(PBCNT)
15
7
4
1
0
RESERVED
CB
CB
I CB I CB
CB
I CB
CB
I
CB
I
PORT 8 DATA DIRECTION REGISTER
(PBDDRI
15
12
11
10
5
1
0
RESERVED
DB
DB I DB
I
DB
I
DB
DB
OB
OB I OB
OB
OB I OB I
PORT 8 DATA RESISTER
(PBDAT)
15
12
11
10
7
3
RESERVED
PB
PB
PB
I
PB I PB
PB
I PB
I
PB
I PB
PB
I
PB
I
PB
I
Figure 3-3. Parallel 1/0 Port Registers
determined by the EMWS bit in the system control register. The RAM is
divided into two parts: parameter RAM and system RAM.
The 576-byte parameter RAM area includes pointers, counters, and registers
used with the serial ports. Any individual locations not required in a given
application may be used as general-purpose RAM.
The 576-byte system RAM is a general-purpose RAM, which may be used as
data RAM or microcode RAM. As data RAM, it can include serial port data
buffers or can be used for other purposes such as a no-wait-state cache for
the M68000 core. As microcode RAM, it can be used to store microcode for
the CP main controller, allowing the development of special protocols or
protocol enhancements, under special arrangement with Motorola.
MC68302 USER'S MANUAL
MOTOROLA
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