9.7 Port 6
9.7.1 Overview
Port 6 is a 7-bit input/output port that is also used for input and output of bus control signals
(
LWR
,
HWR
,
RD
,
AS
,
BACK
,
BREQ
, and
WAIT
). When DRAM is connected to area 3,
LWR
,
HWR
, and
RD
also function as
LW
,
UW
, and
CAS
, or
LCAS
,
UCAS
, and
WE
, respectively. For
details see section 7, Refresh Controller.
Figure 9-6 shows the pin configuration of port 6. In modes 1 to 6 (expanded modes) the pin
functions are
LWR
,
HWR
,
RD
,
AS
, P6
2
/
BACK
, P6
1
/
BREQ
, and P6
0
/
WAIT
. See table 9-11 for
the method of selecting the pin states. In mode 7 (single-chip mode) port 6 is a generic
input/output port.
Pins in port 6 can drive one TTL load and a 30-pF capacitive load. They can also drive a
darlington transistor pair.
Figure 9-6 Port 6 Pin Configuration
9.7.2 Register Descriptions
Table 9-10 summarizes the registers of port 6.
Table 9-10 Port 6 Registers
Initial Value
Address
*
Name
Abbreviation
R/W
Mode 1 to 5
Mode 6, 7
H'FFC9
Port 6 data direction register
P6DDR
W
H’F8
H'80
H'FFCB
Port 6 data register
P6DR
R/W
H’80
H'80
Note:
*
Lower 16 bits of the address.
Port 6
P6 /
P6 /
P6 /
P6 /
P6 /
P6 /
P6 /
6
5
4
3
2
1
0
LWR
HWR
RD
AS
BACK
BREQ
WAIT
Port 6 pins
P6
P6
P6
2
1
0
LWR
HWR
RD
AS
BACK
BREQ
WAIT
Modes 1 to 6
(expanded modes)
(output)
(output)
(output)
(output)
(output)
(input)
(input)
P6
P6
P6
P6
P6
P6
P6
6
5
4
3
2
1
0
Mode 7
(single-chip mode)
(input/output)
(input/output)
(input/output)
(input/output)
(input/output)
(input/output)
(input/output)
(input/output)/
(input/output)/
(input/output)/
262
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