SX Device Programming Specifications Rev 2.2 8 © 2000 Scenix Semiconductor, Inc. All rights reserved. www.scenix.com 2.5 ISP Commands The programmer unit writes a 4-bit command during the four command cycles at the beginning of each
frame, just after the sync cycle. This 4-bit command tells the ISP logic what to do during the remaining
12 cycles of the frame. Table 2.1 lists and describes the programming commands. Codes not listed in
the table are reserved for future expansion. The commands that erase or program the EEPROM registers must be repeated consecutively for a
certain frames in order to work reliably. To determine the minimum required number of repetitions of a  command,  look  in  the  Electrical  Characterization  section  of  the  device  data  sheet  and  find  the minimum time requirement for the operation. Divide this value by the frame period, 0.53 milliseconds,
and round up to the nearest whole number. For example, if you find that the minimum time requirement for an “Erase” operation is 100 ms, divide
100 by 0.53 and round up, and the result is 189. This means that you must repeat the “Erase” command
for at least 189 commands in order to complete the “Erase” operation reliably. “NOPs” can be used in-
between these 189 erase commands. No repetition is necessary to read a register or to increment the memory address pointer. You can
complete one of these operations in just a single frame. Table 2.1 ISP Commands Name Code Description Erase 0000 Erase all EEPROM locations. Read DEVICE Word 0001 Read the Device register. Read FUSEX Word 0010 Read FUSEX word (configuration options) Program FUSEX Word 0011 Program FUSEX word (configuration options) Load Data 0100 Load data word to be programmed into memory. Program Data 0101 Program previously loaded data word into memory. Read Data 0110 Read data word from memory. Increment Address 0111 Increment the program memory pointer by one. NOP 1111 No operation.