Suspend Mode Summary

thereby providing additional user programmable memory space. This feature is enabled by the A20EN instruction and remains enabled until the de- vice is reset. It is important to note that the execu- tion of the A20EN instruction redefines Port 2, bit 1 as a pure output pin with read only characteristics. The state of this pin can be modified only through a valid ‘‘D1’’ command sequence (see Table 1). Once enabled, the A20 logic will process a ‘‘D1’’ com- mand sequence (write to output port) by setting/re- setting the A20 bit on port 2, bit 1 (P2.1) without requiring service from the internal CPU. The host can directly control the status of the A20 bit. At no time during this host interface transaction will the IBF flag in the status register be activated. Table 1 gives several possible GATEA20 command/data se- quences and UPI-C42 responses.

Table 1. D1 Command Sequences

A0	R/W	DB Pins	IBF	A20	Comments

1	W	D1h	0	n(1)	Set A20 Sequence
0	W	DFh	0	1	Only DB1 Is Processed
1	W	FFH(2)	0	n
1	W	D1h	0	n	Clear A20 Sequence
0	W	DDh	0	0
1	W	FFh	0	n
1	W	D1h	0	n	Double Trigger Set
1	W	D1h	0	n	Sequence
0	W	DFh	0	1
1	W	FFh	0	n
1	W	D1h	0	n	Invalid Sequence
1	W	XXh(3)	1	n	No Change in State
0	W	DDh	1	n	of A20 Bit

NOTES:

1.Indicates that P2.1 remains at the previous logic level.

2.Only FFh commands in a valid A20 sequence have no effect on IBF. An FFh issued at any other time will activate IBF.

3.Any command except D1.

The above sequences assume that the GATEA20 logic has been enabled via the A20EN instruction. As noted, only the value on DB 1 (data bus, bit 1) is processed. This bit will be directly passed through to P2.1 (port 2, bit 1).

UPI-C42/UPI-L42

SUSPEND

The execution of the suspend instruction (82h or E2h) causes the UPI-C42 to enter the suspend mode. In this mode of operation the oscillator is not running and the internal CPU operation is stopped. The UPI-C42 consumes s40 mA in the suspend mode. This mode can only be exited by RESET. CPU operation will begin from PC e 000h when the UPI-C42 exits from the suspend power down mode.

#Oscillator Not Running

#CPU Operation Stopped

#Ports Tristated with Weak (E2 – 10 mA) Pull-Up

#Micropower Mode (ICC s 40 mA)

#This mode is exited by RESET