MOTOROLA
MC68349 USER'S MANUAL
4- 37
4.3.5 External Bus Interface Control
The following paragraphs describe the registers that control the I/O pins used with the EBI.
Refer to Section 3 Bus Operation for more information about the EBI. For a list of pin
numbers used with port A and port B, see the pinout diagram in Section 12 Ordering
Information and Mechanical Data. Section 2 Signal Descriptions shows a block
diagram of the port control circuits.
4.3.5.1 PORT A PIN ASSIGNMENT REGISTER 1 (PPARA1). PPARA1 selects between
an address and discrete I/O function for the port A pins. Any set bit defines the
corresponding pin to be an I/O pin, controlled by the port A data and data direction
registers. Any cleared bit defines the corresponding pin to be an address bit as defined in
Table 4-5. The reset value of the PPARA1 bits is the inverse of the state of D29 at reset.
Bits set in this register override the configuration setting of PPARA2. This register can be
read or written at any time.
PPARA1
$015
76543210
PRTA7/
A31
PRTA6/
A30
PRTA5/
A29
PRTA4/
A28
PRTA3/
A27
PRTA2/
A26
PRTA1/
A25
PRTA0/
A24
RESET:
D29
Supervisor Only
4.3.5.2 PORT A PIN ASSIGNMENT REGISTER 2 (PPARA2). PPARA2 selects between
an address and IACK≈ function for the port A pins. Any set bit defines the corresponding
pin to be an IACK≈ output pin (as long as the corresponding PPARA1 bit is cleared). Any
cleared bit defines the corresponding pin to be an address bit (as long as the
corresponding PPARA1 bit is cleared) as defined in Table 4-5. Any set bits in PPARA1
override the configuration set in PPARA2. Since there is no level 0 interrupt, bit 0 has no
function in this register and is reserved by Motorola. This register can be read or written at
any time.
PPARA2
$017
76543210
IACK7/
A31
IACK6/
A30
IACK5/
A29
IACK4/
A28
IACK3/
A27
IACK2/
A26
IACK1/
A25
0
RESET:
00000000
Supervisor Only
The IACK≈ signals are asserted if a bit in PPARA2 is set and the CPU32+ services an
external interrupt at the corresponding level. IACK≈ signals have the same timing as
address strobes.