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CONNECTION WITH EXTERNAL DEVICES
7902 Group User’s Manual
3-4
3.1 Signals required for accessing external devices
Address (A0–A23) output pins
I/O pins for data (D0–D7) at an even- I/O pins for data (D0–D7)
numbered address
I/O pins for data (D8–D15) at an odd-
Programmable I/O port pins (P2)
numbered address
(Note 3)
Input pin for signals related to Ready function (Refer to section “3.3 Ready function.”)
Output pin for read singnal (“L” level is output while data bus is read out.)
Output pin for write signal (“L” level
is output while data is written to an
even-numbered address.)
Output pin for write signal (“L” level
is output while data is written to an
odd-numbered address.) (Note 5)
Output pin for address latch enable signal (This pin indicates address
stabilization and can be used to latch an address.)
Clock
φ1 outputpin(Thispinoutputsasignalwiththesameperiodoffsys.Referto“CHAPTER5.CLOCKGENERATINGCIRCUIT.”)
Input pin for signals related to Hold function (Refer to section “3.4 Hold function.”)
Output pin for signals related to Hold function (Refer to section “3.4 Hold function.”)
Chip select output pins (Refer to section “3.2 Chip select wait controller.”)
External data bus width select input pin (When VSS level is input, 16-bit width is selected; When
VCC level is input, 8-bit width is selected.)
Table 3.1.1 Pins used for accessing external devices
A0–A23
D0–D7
(Note 2)
D8–D15
RDY
RD
BLW
BHW
ALE
φ1
HOLD
HLDA
CS0–CS3
BYTE
(Note 6)
Pin
Access to external devices
External data bus width = 16 bits (BYTE = Vss level)
External data bus width = 8 bits (BYTE = Vcc level)
Undefined (Note 1).
Floating.
(Note 4)
Invalid.
“H” level is output.
(Note 4)
“L” level is output.
Invalid.
“H” level is output.
Programmable I/O port pin (P33)
Access to internal
devices
Output pin for write signal (“L” level
is output while data is written to the
external area.)
Notes 1: Address outputs at access to internal areas can be fixed by software. (Refer to section “3.2.4
Address output selection.”)
2: When area CS2 is accessed with the external data bus width = 8 bits, by software, the address
output (LA0–LA7) and the data input/output (D0–D7) can be performed with the time-sharing method.
(Refer to section “3.2.2 External bus operations.”)
3: When an area with the external data bus width = 8 bits is accessed by software, these pins are
placesd in the floating state. (See Figure 2.2.6.)
4: This applies only when the external data bus width = 16 bits (BYTE = Vss level).
5: When an area with the external data bus width = 8 bits is accessed by software, “H” level is output.
(See Figure 2.2.6.)
6: Do not change the input level to this pin while the microcomputer is operating.
The data bus width selected by the input to pin BYTE is valid only for the external areas. (See
Figure 3.1.2.) When an internal area is accessed, the data bus width is always fixed to 16 bits.
When BYTE = Vss, the external data bus width of 8 bits can independently be selected by
software for each of areas CS1–CS3. (Refer to section “3.2 Chip select wait controller.”)
7: For details of each signal and input/output timings, refer to each reference and section “Appendix
9. M37902FGCGP electrical characteristics” and “Appendix 10. M37902FGMHP electrical
characteristics.”