h8s-2138 Renesas Electronics Corporation., h8s-2138 Datasheet - Page 591

• Manufacturer Part Number: h8s-2138
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

Table 17.6 Host Interface Operation
17.3.3
The A20 gate signal can mask address A20 to emulate an addressing mode used by personal
computers with an 8086 * -family CPU. In slave mode, a regular-speed A20 gate signal can be
output under firmware control, or a fast A20 gate signal can be output under hardware control.
Fast A20 gate output is enabled by setting the FGA20E bit (bit 0) to 1 in HICR (H'FFF0).
Note: * Intel microprocessor.
Regular A20 Gate Operation: Output of the A20 gate signal can be controlled by an H'D1
command followed by data. When the slave processor receives data, it normally uses an interrupt
routine activated by the IBF1 interrupt to read IDR1. If the data follows an H'D1 command,
software copies bit 1 of the data and outputs it at the gate A20 pin.
Fast A20 Gate Operation: When the FGA20E bit is set to 1, P81/GA20 is used for output of a
fast A20 gate signal. Bit P81DDR must be set to 1 to assign this pin for output. The initial output
from this pin will be a logic 1, which is the initial value. Afterward, the host processor can
manipulate the output from this pin by sending commands and data. This function is available
CS2
CS2
CS2
CS2
1
0
CS1
CS1
0
1
CS1
CS1
A20 Gate
IOR
IOR
IOR
IOR
0
1
0
1
IOW
IOW
IOW
IOW
0
1
0
1
0
1
0
1
HA0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Operation
Setting prohibited
Setting prohibited
Data read from output data register 1 (ODR1)
Status read from status register 1 (STR1)
Data write to input data register 1 (IDR1)
Command write to input data register 1 (IDR1)
Idle state
Idle state
Setting prohibited
Setting prohibited
Data read from output data register 2 (ODR2)
Status read from status register 2 (STR2)
Data write to input data register 2 (IDR2)
Command write to input data register 2 (IDR2)
Idle state
Idle state
Section 17 Host Interface [H8S/2138 Group]
Rev. 4.00 Jun 06, 2006 page 537 of 1004
REJ09B0301-0400