Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement - Manual (Page 109)

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
109
(TSL: DPS.5) is set to 1, the SEL bit (DPS.0) is automatically toggled every time one of the following DPTR instructions is executed.
Thus, depending upon the state of the SEL1 bit (DPS.3), the active data pointer toggles between the DPTR0, DPTR1 pair or the DPTR2,
DPTR3 pair.
Auto-Toggle (if TSL=1)
INC DPTR
MOV DPTR, #data16
MOV DPTR, #data24
MOVC A, @A+DPTR
MOVX A, @DPTR
MOVX @DPTR, A
When the autoincrement/decrement bit (AID: DPS.4) is set to 1, the active data pointer is automatically incremented or decremented
every time one of the following DPTR instructions is executed.
Autoincrement/Decrement (if AID=1)
MOVC A, @A+DPTR
MOVX A, @DPTR
MOVX @DPTR, A
When used in conjunction, the autotoggle and auto-increment/decrement features can produce very fast routines for copying or mov-
ing data. For example, the basic loop needed to copy data between two different MOVX data memory ranges can be simplified to the
following code:
;R6:R7 are loop variables controlling copy length
LOOP:
MOVX A, @DPTR ;read from source
MOVX @DPTR, A ;write to destination
DJNZ R7, LOOP
DJNZ R6, LOOP
The advantage to having four data pointers is that the second pair of data pointers can be selected for use whenever the first pair is
already in use. This allows the application to: 1) conserve stack space that would normally be needed to save the data pointer(s) prior
to another task that needs the data pointer(s), and 2) respond more quickly to a task that requires use of the data pointer(s).
For example, suppose that a pair of data pointers are being used to load data into Ethernet transmit buffer memory. While loading trans-
mit buffer memory, an Ethernet receive interrupt request occurs that needs servicing. Servicing the interrupt requires that a received
packet be transferred from internal data buffer memory to external data memory. Normally, the dual data pointer values would be
pushed onto the stack and restored following the interrupt service routine to resume the loading of transmit buffer memory. With an
additional pair of data pointers (DPTR2 and DPTR3) with which to work, the application need not push the current data pointer values
onto the stack; it can simply select the second pair.
ADDENDUM TO SECTION 7: POWER MANAGEMENT
The DS80C400 supports the general power-management features of the DS87C520. Exceptions are noted as follows.
Precision Voltage Monitor
The DS80C400 does incorporate a precision bandgap reference, but unlike previous high-speed microcontrollers, it requires dual
power supplies. The core power supply (V
CC1
) is a nominal 1.8V supply, and the I/O power supply (V
CC3
) is a nominal 3.3V supply.
Therefore, two sets of voltage thresholds (one for each supply) have been implemented. The respective power-fail and reset voltage
thresholds for V
CC1
are V
PFW1
and V
RST1
, while the V
CC3
thresholds are V
PFW3
and V
RST3
. The minimum, typical, and maximum values
for these thresholds are specified in the DC Electrical Characteristics section of the DS80C400 data sheet.
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