HD6477021X20V Renesas Electronics America, HD6477021X20V Datasheet - Page 168
HD6477021X20V
Manufacturer Part Number
HD6477021X20V
Description
MCU 5V 32K PB-FREE 100-TQFP
Manufacturer
Renesas Electronics America
Series
SuperH® SH7020r
Datasheet
1.HD6417020SVX12IV.pdf
(511 pages)
Specifications of HD6477021X20V
Core Processor
SH-1
Core Size
32-Bit
Speed
20MHz
Connectivity
EBI/EMI, SCI
Peripherals
DMA, POR, PWM, WDT
Number Of I /o
32
Program Memory Size
32KB (32K x 8)
Program Memory Type
OTP
Ram Size
1K x 8
Voltage - Supply (vcc/vdd)
4.5 V ~ 5.5 V
Oscillator Type
Internal
Operating Temperature
-20°C ~ 75°C
Package / Case
100-TQFP, 100-VQFP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Eeprom Size
-
Data Converters
-
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
HD6477021X20V
Manufacturer:
Renesas Electronics America
Quantity:
10 000
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8.5.6
The BSC has a function for controlling DRAM refreshing. By setting the refresh mode bit
(RMODE) in the refresh control register (RCR), either CAS-before-RAS refresh (CBR) or self-
refresh can be selected. When no refresh is performed, the refresh timer counter (RTCNT) can be
used as an 8-bit interval timer.
CAS-Before-RAS Refresh (CBR): A refresh is performed at an interval determined by the input
clock selected in the clock select bits 2–0 (CKS2–CKS0) of the refresh timer control/status
register (RTCSR) and the value set in the refresh time constant register (RTCOR). Set the values
of RTCOR and CKS2–CKS0 so they satisfy the refresh interval specifications of the DRAM being
used.
To perform a CBR refresh, clear the RMODE bit of the RCR to 0 and then set the refresh control
bit (RFSHE) bit to 1. Also write in the required values to RTCNT and RTCOR. When the clock is
thereafter selected in the CKS2–CKS0 bits of the RTCSR, the RTCNT will begin to increment
from its current value. The RTCNT value is constantly compared to the RTCOR value and the
CBR refresh is performed when they match. The RTCNT is simultaneously cleared to H'00 and
incrementing begins again.
When the clock is selected in the CKS2–CKS0 bits, the RTCNT immediately begins to increment
from its current value. This means that when the RTCOR cycle is set after the CKS2–CKS0 bits
are set, the RTCNT count may already be higher than the RTCOR cycle. When this occurs, the
RTCNT will overflow once (H'FF goes to H'00) and incrementing will start again. Since the CBR
148 RENESAS
AD15–
A21–
RAS
CAS
AD0
CK
A0
Refresh Control
T
p
Row address
T
r
DRAM access
address 1
Column
Figure 8.28 RAS Up Mode
T
c
Data 1
address 2
Column
T
c
External memory
Data 2
space access
External memory
memory data
T1
External
address
T
p
DRAM access
Row address
T
r
address 3
Column
T
c
Data 3
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