7721 datasheet(537/577 Pages) RENESAS

537 / 577 page

APPENDIX

Appendix 9. 7721 Group Q & A

7721 Group User’s Manual

17–74

In the wait mode, DRAM refresh function does not operate, but the watchdog timer, timer A, and

timer B operate. Accordingly, DRAM can be refreshed by using these timers and ports.

(1) Method using watchdog timer

Return from the wait mode by the watchdog

timer interrupt. Control ports P104, P105 by

____

software and perform the CAS-before-RAS-

refresh.

Example 1: A case in 1024 refresh cycles, every 16.4 ms, f(XIN) = 16 MHz, watchdog timer

count source = f32

•DRAM refresh is performed 256 times. This refresh is performed by every

watchdog timer interrupt. (See flow chart .)

Interval of watchdog timer interrupt

f(XIN)

25 MHz

16 MHz

f32 selected

2.621 ms

4.096 ms

f512 selected

41.943 ms

65.536 ms

(1/2)

DRAM validity bit

(bit 7 at address 6416)

Bits 4, 5 of port P10 register

(address 1616)

← “1”

WIT instruction

Wait mode completed ?

Wait mode

DRAMC stopped

Watchdog timer count

source: f32 selected

Ports P104, P105:

“H” level output

Note: By using 1 bit of RAM, judge

whether this interrupt is for return

from the wait mode or for refresh.

256 times ?

RTI

Return to main routine

← “1”

Bits 4, 5 of port P10 direction

← “1”

← “0”

Watchdog timer frequency

select bit (bit 0 at address 6116)

Main routine

Flow chart

Watchdog timer

interrupt routine

← “0”

Bit 4 of port P10 register

(address 1616)

← “0”

Bit 5 of port P10 register

(address 1616)

← “1”

Bit 4 of port P10 register

(address 1616)

← “1”

Bit 5 of port P10 register

(address 1616)

Port P105 (RAS)

“H” level output

Port P104 (CAS):

“H” level output

Port P105 (RAS):

“L” level output

Port P104 (CAS):

“L” level output

Port P105 (RAS):

“H” level output

7721 Datasheet(PDF) 537 Page - Renesas Technology Corp

7721 Datasheet(HTML) 537 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL