
HARDWARE
1-42
3886 Group User’s Manual
[Data Bus Buffer Status Register 0, 1
(DBBSTS0, DBBSTS1)] 002916, 002C16
The data bus buffer status registers 0 and 1 consist of eight bits.
Bits 0, 1, and 3 are read-only bits and indicate the condition of the
data bus buffer. Bits 2, 4, 5, 6, and 7 are user definable flags
which can be set by program, and can be read/written. This regis-
ter can be read from the host CPU when the A0 pin is set to “H”
only.
Bit 0: Output buffer full flag OBF0, OBF1
When writing data to the output data bus buffer, these flags are
set to “1”. When reading the output data bus buffer from the host
CPU, these flags are cleared to “0”.
Bit 1: Input buffer full flag IBF0, IBF1
When writing data from the host CPU to the input data bus
buffer, these flags are set to “1”. When reading the input data
bus buffer from the slave CPU side, these flags are cleared to
“0”.
Bit 3: A0 flag A00, A01
When writing data from the host CPU to the input data bus
buffer, the level of the A0 pin is latched.
[Input Data Bus Buffer Register 0, 1 (DBBIN0,
DBBIN1)] 002816, 002B16
Data on the data bus is latched to DBBIN by writing request from
the host CPU. Data of DBBIN can be read from the data bus
buffer registers (address 002816 or 002B16) on SFR.
[Output Data Bus Buffer Register 0, 1
(DBBOUT0, DBBOUT1)] 002816, 002B16
When writing data to the data bus buffer registers (address 002816
or 002B16) on SFR, data is set to DBBOUT. Data of DBBOUT is
output from the host CPU to the data bus by performing the read-
ing request when the A0 pin is set to “L”.
[Port control Register 2 (PCTL2)] 002F16
Even if the data bus buffer function is enabled, both P42 and P43
function as ports when the OBF00 output enable bit (bit 3 of ad-
dress 2A16) or the OBF01 output enable bit (bit 4 of address 2A16)
is “0”. Ports P42 and P43 are cleared to “0” by changing the input
buffer full flag 0 (bit 1 of address 2916) from “1” to “0” under the fol-
lowing conditions: the port output P42/P43 clear function selection
bit (bit 7) is set to “1”, both ports are in the output mode of the port
function, and both port latches are “1”.
FUNCTIONAL DESCRIPTION