Junior Interface card – Retro Computing

The Interface card adds more memory (2x EPROM 2716, 1K RAM with 2x 2114), cassette interface, TTY interface, VIA 6522 interface.
Inspired by the KIM-1 and the Micro ADE cassette motor control. Note that the hardware TTY echo is now a jumper!

Software PM (Print Monitor, a serial interface monitor) and TM (Tape Monitor, to load/save KIM-1 compatible files on tape) and PM (Print Monir Extended).
EPROM ESS507 has PM, ESS507N has PM + PME, ESS506 has TM.

The bipolar ROM 82S33 has the name ESS508, it is used to decode memory for the various devices on the expansion card. A real problem device when constructing a new Junior!
See the Programming a 82S23 page how to program the 82S23.

Circuit diagram part 1, ROM, RAM, VIA

Circuit diagram part 2, TTY interface, audio cassette interface

	the fully fledged Junior Computer
	the junior reaches maturity
	Listing in Micro Ade format of TM PM PME from book 2
	ESS508, the 82S23 PROM memory decoder
	ESS508 82S23 ROM
	Sources of TM PM PME, TASM format, delivers binaries identical to the published listings
	Alternative source of PM, delivers binary identical to listing
	TM ESS506 ROM 2K
	PM ESS507 (without PME) ROM 2K
	PM PME ESS507n ROM 2K
	ESS507n TM + PM + PME in a 4K ROM format
	junior interface TM ROM 2K old dump, see note below

The ROMS you need for an original Interface card are TM 506 and PM PME 507n.

Have a look at the Elektor Articles and Books page for a mullti-lingual overview of all publications on Elektor/Elektuur Junior and more.

Note that in old dumps of ROMs of TM there is a (harmless) error. On location it should be
0C21 C9 41 CMP #$41 ;IGNORE 3A…40
Instead is found
0C21 C9 14
which means the check is also OK with correct input. Perhaps this error was in the original ROM already and never noticed!

0717   0C19             ;*** ASCHEX ***
0718   0C19             ;CONVERT AN ASCII CHARACTER TO A HEX DATA NIBBLE.
0719   0C19             ;1) RETURN WITH CONVERTED HEX NUMBER IN ACCU
0720   0C19             ;2) N = 1, IF NOT VALID HEX NUMBER
0721   0C19             ;3) Z = 1, IF VALID HEX NUMBER
0722   0C19             ;4) *** ASCHEX IS ALSO USED IN THE PRINTER SOFTWARE ***
0723   0C19 C9 30       ASCHEX	CMP #$30		;IGNORE 00...2F
0724   0C1B 30 0C               BMI NOTVAL
0725   0C1D C9 3A               CMP #$3A
0726   0C1F 30 0B               BMI VALID
0727   0C21 C9 41               CMP #$41 		;IGNORE 3A...40
0728   0C23 30 04               BMI NOTVAL
0729   0C25 C9 47               CMP #$47 		;IGNORE 47...7F
0730   0C27 30 03               BMI VALID

Interface card PCB front (note not on scale!)

Interface card PCB back (note not on scale!)

Interface card layout