
CL-PD6710/’22
ISA–to–PC-Card Host Adapters
May 1997
79
PRELIMINARY DATA SHEET v3.1
USING GPSTB PINS FOR EXTERNAL PORT CONTROL
(CL-PD6722 only)
12.2 Example Implementations of GPSTB-Controlled Read and Write Ports
Figure 12-1. Example GPSTB Write Port (Extension Control 2 bits 4:3 are ‘10’)
In this mode,
Extension Control 2
register bit 4 is set to ‘1’ enabling the GPSTB pin to function as a write
strobe. Writes to the respective extended index 0Ah cause the respective GPSTB to go active (low) for
the duration of the system’s IOW* pulse.
On writes, data is written to both the external latch and the internal shadow copy of the
External Data
register. A read of the respective extended index 0Ah would produce the last value written to the latch.
Connection of the ISA bus PWRGOOD signal to the external latch ensures that the latch assumes all ‘0’s
at its outputs when the CL-PD67XX is reset.
Figure 12-2. Example GPSTB Read Port (Extension Control 2 bits 4:3 are ‘01’)
In this mode,
Extension Control 2
register bit 3 is set to ‘1’, enabling the respective GPSTB pin to function
as a read strobe. Reads from the corresponding extended index 0Ah cause GPSTB to go active (default
active level is low) for the duration of the system’s IOR* pulse.
NOTE:
Data is still written to the shadowed
External Data
register on writes to Extended Index 0Ah but is not
visible.
IOW*
IOW*
SD[15:0]
SD[15:0]
GPSTB
Latch
CK
O0
D
RES
EXT_WR*
SD[15:8]
(16-bit bus)
General-
Purpose
Outputs
O7
PWRGOOD
Pull-up
Pull-up resistor, or set Extension Control 2 bit 2 to ‘1’ for totem-pole output.
(for example, ’374)
CL-PD6722
IOR*
IOR*
SD[15:0]
SD[15:0]
GPSTB
Tristate Buffer
(for example, ’244)
D7
O
D0
OE
EXT_RD*
SD[15:8]
(16-bit bus)
General-
Purpose
Inputs
Pull-up resistor, or set Extension Control 2 bit 2 to ‘1’ for totem-pole output.
Pull-up
CL-PD6722